<PAGE>   1
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D. C. 20549
                                    Form 10-K

[X]      ANNUAL REPORT PURSUANT TO SECTION 13 OR 15 (D) OF THE SECURITIES
         EXCHANGE ACT OF 1934
 
                     For fiscal year ended December 31, 1998
                                       or

[ ]      TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 (D) OF THE SECURITIES
         EXCHANGE ACT OF 1934

         For transition period from               to
                                    --------------  --------------

                         Commission File Number 0-13655

                            SECURITY BANC CORPORATION
                          State of Incorporation: Ohio
                I.R.S. Employer Identification Number: 31-1133284
                            40 South Limestone Street
                Springfield, Ohio 45502           (513) 324-6800

           Securities register pursuant to Section 12 (g) of the Act:
                         Common Stock, $1.5625 Par Value


Indicate by check mark whether the registrant (1) has filed all reports required
                         to be filed by Section 13 or 15 (d) of the Securities
                         Exchange Act of 1934 during the preceding 12 months,
                         and (2) has been subject to such filing requirements
                         for the past 90 days. Yes  X   No
                                                   ---     ---

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405
            of Regulation S-K (229.405 of this chapter) is not contained herein,
            and will not be contained, to the best of registrant's knowledge, in
            definitive proxy or information statements incorporated by reference
            in Part III of this Form 10-K or any amendment to this Form 10-K.
            Yes  X   No
                ---     ---

The aggregate market value of the voting stock held by non-affiliates of the
Registrant was $559,655,550.00 as of January 10, 1999.

The number of shares outstanding of the Registrant's common stock, $1.5625 par
value per share as of January 21, 1999 was 12,166,425 shares.

DOCUMENTS INCORPORATED BY REFERENCE
Portions of the Annual Shareholder's Report for the year ended December 31, 1998
are incorporated by reference into Parts I and II.

Portions of the Proxy Statement for the Annual Shareholder's Meeting to be held
April 20, 1999 are incorporated by reference into Part III.

<PAGE>   2
<TABLE>
                   SECURITY BANC CORPORATION AND SUBSIDIARIES

                                      INDEX
<CAPTION>
                                                                       Page No.
                                                                       --------
<S>            <C>                                                     <C>
Part I
     Item  1.  Business..............................................  3 thru 17

     Item  2.  Properties............................................         18

     Item  3.  Legal Proceedings.....................................         19

     Item  4.  Submission of Matters to a Vote of Security Holders...         19

Part II
     Item 5.   Market for Registrant's Common Equity and Related
                       Shareholder Matters...........................         19

     Item 6.   Selected Financial Data...............................         19

     Item 7.   Management's Discussion and Analysis of Financial
                       Condition and Results of Operations...........         19

     Item 8.   Financial Statements and Supplementary Data...........         19

     Item 9.   Changes in and Disagreements with Accountants on
                       Accounting and Financial Disclosure...........         19

Part III
     Item 10.  Directors and Executive Officers of The Registrant....         20

     Item 11.  Executive Compensation................................         20

     Item 12.  Security Ownership of Certain Beneficial Owners and
                       Management....................................         21

     Item 13.  Certain Relationships and Related Transactions........         21

Part IV
     Item 14.  Exhibits, Financial Statement Schedules and Reports
                       on Form 8-K................................... 21 thru 22

Signatures...........................................................         23
</TABLE>

                                       -2-
<PAGE>   3
PART I

ITEM 1.      BUSINESS

        Security Banc Corp. (Registrant or Company) was organized in 1985 under
        the laws of The State of Ohio. The Executive Office of the registrant is
        located in Springfield, Ohio. It is a Bank Holding Company as defined in
        the Bank Holding Company Act of 1956, as amended, and is registered as
        such with the Board of Governors of the Federal Reserve System.
        Registrant has three subsidiaries, The Security National Bank and Trust
        Co. (Security), Citizens National Bank (Citizens), and Third Savings and
        Loan Company, (Third).

        The Security National Bank and Trust Co. was organized under the
        statutes of The United States as the result of an agreement to merge The
        Guardian Bank of Springfield, Ohio, with and into The New Carlisle
        National Bank under the title of The Security National Bank. The
        agreement to merge was finalized and given approval by the Office of The
        Comptroller of the Currency on October 1, 1969. The Bank was granted the
        authority to act as a fiduciary as of May 30, 1978, thereby, changing
        the name of the Association to "The Security National Bank and Trust
        Co." The Bank's main office is located at 40 South Limestone Street,
        Springfield, Ohio.

        On September 30, 1996, the Company merged with CitNat Bancorp, Inc., a
        $140 million bank holding company headquartered in Ohio, in a
        transaction accounted for as a pooling of interest.

        On October 21, 1996, the Company acquired all of the outstanding shares
        of Third Financial Corporation for $41 million. The acquisition was
        accounted for using the purchase method of accounting.

        Security and Citizens are subject to primary supervision, examination,
        and regulation by The Comptroller of the Currency. Third is subject to
        primary supervision, examination, and regulation by The Office of Thrift
        Supervision. Security and Citizens are members of The Federal Reserve
        System and are subject to the applicable provisions of The Federal
        Reserve System and are subject to the applicable provisions of the
        Federal Reserve Act and Regulations. Deposits of the Company are insured
        by The Federal Deposit Insurance Corporation (FDIC) to the maximum
        extent permitted by law.

        Security was the parent of the Security Community Urban Redevelopment
        Corporation. The subsidiary was an Ohio Corporation organized in 1975
        and dissolved in 1997. It was organized solely to own Security's main
        office building. Presently, Security owns the Main Office building.

        All of the Company's banking centers are located in Champaign, Clark,
        Fayette, Greene, Madison and Miami Counties in the state of Ohio.

                                       -3-
<PAGE>   4
BUSINESS--CONTINUED

As of December 31, 1998, the Company's consolidated total assets rounded to the
nearest thousand, were $883,500,000 including total loans of $562,005,000. On
that date, total deposits were $708,853,000 and capital accounts totaled
$118,129,000.

The Company's subsidiaries provide full service banking to individuals as well
as to industry and governmental subdivisions through each of its twenty-four
banking centers.

The Company's subsidiaries have made a strong impact on all the counties it
serves through a great variety of services, including personal checking accounts
and savings programs, certificates of deposit, the Money Market accounts, C/D's
and Individual Retirement Accounts.

A broad range of credit programs for all retail customers includes mortgage
loans, credit card banking under the VISA designation, installment loans, and
secured and unsecured personal loans.

The banking services provided to commercial customers and government include
maintenance of demand and time deposit accounts and certificates of deposit.
Available are all types of commercial loans, including loans under lines of
credit and revolving credit, term loans, real estate mortgage loans and other
specialized loans including accounts receivable financing. The Subsidiaries
further serve the requirements of large and small industrial and commercial
enterprises in the Springfield metropolitan area and elsewhere by providing
financial counseling, automated payroll programs, cash management, and other
automated services.

The subsidiaries' Commercial Banking Division is organized to serve the needs of
the corporate customers by handling business and commercial mortgages, corporate
deposits and other corporate financial services.

The Consumer Banking Divisions, which encompasses the Credit Card and
Installment Loan Departments, serves individual as well as corporate customers.
The Residential Mortgage Loan Departments provides conventional as well as
adjustable rate mortgage loans to individuals. Each Subsidiary manages the
investment of funds for their institution using U. S. Government and agency
securities, municipal (tax exempt) securities, as well as Federal Funds and
certificates of deposit of U. S. banks and savings and loans. Each Subsidiary,
in consultation with others, sets the rates on their liability products
including purchased federal funds.

Complete fiduciary services are available to individuals, charitable
institutions, commercial customers and government agencies through Security's
Trust Division. The Personal Trust Department serves as investment agent and
custodian for securities portfolios of individuals, as trustees for living and
testamentary trusts and as executor and administrator of probate estates. The
Corporate Trust Department serves as Trustee for corporate and municipal bond
issues, and as registrar for securities. The Institutional Services Department
provides employee benefit plan fund management for qualified retirement plans
and investment management and securities custody services for not-for-profit
institutions.

There are over a half dozen commercial banks in Springfield, Clark County and
adjoining counties, furnishing general banking services and thus providing
strong competition to the Company. The Company competes for deposits not only
with commercial banks in its area, but also with building and loan associations
and other non-bank competitors, such as brokerage houses. In addition to the
competition described above, the Company competes in various areas of service
offered to individuals, industry and government with Banks in Southwestern Ohio,
many of which possess greater financial resources than the Company.

                                       -4-
<PAGE>   5
BUSINESS--CONTINUED

The earnings of the Company are affected by general economic conditions as well
as, by the monetary policies of the Federal Reserve Board. Such policies, which
have the effect of regulating the national supply of Bank reserves and Bank
credit, can have a major affect upon the source and cost of loanable and
investable funds and the rates of return earned on loans and investments. Among
the means available to the monetary authorities to influence the size and
distribution of Bank reserves are open market operations by the Board of
Governors of the Federal Reserve System, changes in cash reserve requirements
against member bank deposits, and limitations on interest rates which member
banks may pay on most time and savings deposits.

Material Changes and Developments
---------------------------------

There were no material changes or developments during 1998 in the business done
by the Company.

Regulation and Supervision
--------------------------

Security and Citizens, as national banks, are subject to regulation by the
Comptroller of the Currency, The Board of Governors of the Federal Reserve
System and The Federal Deposit Insurance Corporation. Third, as a savings and
loan, is subject to regulation by the Office of Thrift Supervision and The
Savings Association Insurance Fund. The Company and any subsidiaries which it
may hereafter have will be affiliates of the Company within the meaning of the
Federal Reserve Act. As affiliates, the Company and any such subsidiaries are
subject to certain restrictions on loans by the subsidiaries, on investments by
the subsidiaries in their stock or securities or on its taking such stock and
securities as collateral for loans to any borrower. The Company and any such
subsidiaries, as affiliates of the Company are also subject to certain
restrictions with respect to engaging in the underwriting and public sale and
distribution of securities. Neither the Company nor any such subsidiaries may,
for example, engage in such transactions with respect to securities of the
company unless such securities are registered under the Securities Act of 1993
or any exemption from such registration is available. In addition, any such
affiliates of the Bank will be subject to examination at the discretion of
supervisory authorities.

The Company, as a Bank Holding Company, is subject to the restrictions of the
Bank Holding Company Act of 1956 as amended. This Act first provides that the
acquisition of control of a bank is subject to the prior approval of the Board
of Governors of the Federal Reserve System. In the future, the Company will be
required to obtain the prior approval of the Federal Reserve Board before it may
acquire, for its individual account all, or substantially all, of the assets of
any bank, or acquire ownership or control of any voting securities of any Bank,
if after giving effect to such acquisition, the Company would own or control
more than 5% of the voting shares of such bank. The Act does not permit the
Federal Reserve Board to approve the acquisition by the Company or any
subsidiary for their own account, of any voting shares of, or interest in, or
all, or substantially all, of the assets, of any bank located in a state other
than Ohio, unless such acquisition is specifically authorized by the statutes of
the state in which such bank is located.

The Bank Holding Company Act limits the activities which may be engaged in by
the Company and its subsidiaries to ownership of banks and those activities
which the Federal Reserve Board has deemed or may in the future find, by order
of regulations, to be so closely related to the banking or managing or
controlling banks as to be a proper incident thereto.

                                       -5-
<PAGE>   6
BUSINESS--CONTINUED

Those activities presently authorized by the Federal Reserve Board include the
following general activities: (1) the making or acquiring of loans or other
extensions of credit: (2) operating as an industrial bank, Morris Plan Bank, or
industrial loan company according to state law without the accepting of demand
deposits and without the making of commercial loans: (3) the servicing of loans
for any person: (4) performing certain trust functions: (5) acting with certain
limitations as investment or financial advisor: (6) leasing personal property
and equipment: (7) the making of equity and debt investments in projects or
corporations designated primarily to promote community welfare: (8) providing
bookkeeping and data processing services for the internal operations of the Bank
Holding Company and its Subsidiaries: and providing to others, data processing
and transmission services and facilities for banking, financial or related
economic data: (9) acting as insurance agent or broker under certain
circumstances and with respect to certain types of insurance: (10) acting as
underwriter for credit life insurance and credit accident and health insurance
which is directly related to extensions of credit by the Bank Holding Company
System: (11) providing limited courier services for the internal operations of
the Holding Company, for checks exchanged among banking institutions, and for
audit and accounting media of a banking or financial nature used in processing
such media: (12) providing management consulting advice to non-affiliated banks
under certain limitations; (13) the retail sale of money orders with a face
value of $1,000 or less, of travelers checks and of U. S. Savings Bonds: (14)
performing appraisals of real estate: (15) providing securities brokerage
services, (restricted to buying and selling securities solely as agent for
customers), related securities activities and incidental activities: (16)
underwriting and dealing in government obligations and money market instruments:
(17) foreign exchange advisory and transactional services: and (18) acting as
futures commission merchant. For details and limitations on these activities,
reference should be made to Regulation Y of the Federal Reserve Board, as
amended. Further, under the 1970 amendment of this Act and the regulations of
the Federal Reserve Board, the Company and its subsidiaries will be prohibited
from engaging in certain tie-in arrangements in connection with any extension of
credit or provisions of any property or service.

Employees
---------

As of December 31, 1998, there were no full time employees of the Registrant.
Affiliates of the Registrant had full time equivalent employees of 327 of whom
59 were officers.

Statistical Information
-----------------------

Pages 7 through 17 contain statistical information on the Company and its
subsidiaries.

                                       -6-
<PAGE>   7
BUSINESS--CONTINUED

Investment Portfolio
--------------------

The following table sets forth the carrying amount of investment securities at
the dates indicated. (000s)

<TABLE>
<CAPTION>
                                                              December 31
                                                              -----------

                                                       1998         1997         1996
                                                   --------     --------     --------
<S>                                                <C>          <C>          <C>
Available for Sale Investments:
    U. S. Treasury                                 $  7,506     $116,011     $136,020
    U. S. Government Agencies and Corporations       59,650       12,887       15,419
    Corporate Bonds                                       0          250        1,464
    Mortgage Backed Securities                       67,425          135        2,387
    Equity Securities                                   229          356          485
                                                   --------     --------     --------
Total Available for Sale Investments               $134,810     $129,639     $155,775
Held to Maturity Investments:
    State and Political Subdivisions                 26,859       13,262       28,530
    Mortgage Backed Securities                        2,332        3,484        4,010
    Federal Reserve Stock and Other                   3,323        2,794        2,668
                                                   --------     --------     --------
Total Held to Maturity Investments                 $ 32,514     $ 19,540     $ 35,208
                                                   --------     --------     --------
Total Carrying Value of Investments                $167,324     $149,179     $190,983
                                                   ========     ========     ========
</TABLE>

The following table sets forth the redemption/ maturities of debt securities at
December 31, 1998 and the weighted average yields of such securities (calculated
on the basis of the cost and effective yields weighted for the scheduled
redemption/maturity of each security). Callable securities are shown at their
earliest call date. Tax-equivalent adjustments (using a 35% rate) have been made
in calculating yields on obligations of state and political subdivisions. (000)s

<TABLE>
<CAPTION>
                                                                             Maturing
                                    --------------------------------------------------------------------------------------------
                                                                After One                After Five
                                          Within                  Within                 But Within                  After
                                         One Year               Five Years                Ten Years                Ten Years
                                    Amount      Yield        Amount     Yield        Amount       Yield       Amount       Yield
                                    ------      -----        ------     -----        ------       -----       ------       -----
<S>                                 <C>         <C>          <C>        <C>          <C>          <C>         <C>          <C>
Available for Sale Investments:
    U. S. Treasury                  $ 5,485     5.73%        $2,021     5.40%        $     0         0%       $      0        0%
    U. S. Govt. Agencies and Corp.   57,937     5.91%         1,713     6.10%              0         0%              0        0%
    Mortgage Backed Securities            0        0%             0        0%          4,881      5.65%         62,544     6.40%

Held to Maturity Investments:
States and Political Subdivisions     2,294     6.43%         5,701     6.89%         17,180      7.05%           1684     6.93%
Mortgage-backed Securities                0        0%           501     6.75%              0         0%          1,831     6.48%
                                    -------     ----         ------     ----         -------      ----         -------     ---- 
                                    $65,716     5.91%        $9,936     6.44%        $22,061      6.74%        $66,059     6.42%
</TABLE>

                                      -7-
<PAGE>   8
BUSINESS--CONTINUED

Types of Loans
--------------

The following table summarizes consolidated loans by major category for the five
years ending December 31. (000s)

<TABLE>
<CAPTION>
                                                                  December 31
                                             1998         1997         1996         1995         1994
                                             ----         ----         ----         ----         ----
<S>                                      <C>          <C>          <C>          <C>          <C>     
          Commercial and Agriculture     $285,958     $252,053     $212,046     $170,905     $166,116
          Real Estate                     252,609      225,791      234,935      132,402      130,753
             Consumer                      78,375       84,161       93,787       93,263       98,129
                                         --------     --------     --------     --------     --------
          TOTAL LOANS                    $616,942     $562,005     $540,768     $396,570     $394,998
                                         ========     ========     ========     ========     ========
</TABLE>

Non-accrual loans totaled $2,154,000 and $3,417,000 as of December 31, 1998 and
1997 respectively.

                                       -8-
<PAGE>   9
BUSINESS--CONTINUED

The following table shows the maturity of loans (excluding those in non accrual
status) outstanding as of December 31, 1998. Also provided are the amounts due
after one year classified according to the sensitivity to changes in interest
rates. (000s)

<TABLE>
<CAPTION>
                                                                MATURING
                                        --------------------------------------------------------
                                          Within       After One But          After
                                        One Year   Within Five Years     Five Years        Total
                                        --------   -----------------     ----------        -----
<S>                                     <C>        <C>                   <C>            <C>
Commercial, Ag                          $ 82,013            $ 44,934       $107,436     $234,383
Real Estate-Construction                   8,401               1,240          4,439       14,080
All Other Loans                           28,880              82,650        254,795      366,325
                                        --------            --------       --------     --------
Total Loans                             $119,294            $128,824       $366,670     $614,788
                                        ========            ========       ========     ========

Loans maturing after one year with:
Fixed Interest  rate                                        $106,222       $207,968
Variable Interest                                             22,602        158,702
                                                            --------       --------
                                                            $128,824       $366,670
                                                            ========       ========
</TABLE>

RISK ELEMENTS
-------------

Interest on loans is normally accrued at the rate agreed upon at the time each
loan was negotiated. It is the Bank's policy to discontinue accrual of interest
on commercial and mortgage loans when there is a clear indication that the
borrower's cash flow may not be sufficient to meet payments as they become due.
When a consumer loan is uncollectable, the loan is charged off. If there is
collateral, it is secured and disposed of. In regards to paragraph 6i of SFAS
118, the amounts are immaterial and, therefore, not disclosed. The following
table presents data concerning loans at risk at the end of each period. (000s).

<TABLE>
<CAPTION>
                              1998       1997       1996       1995       1994
                              ----       ----       ----       ----       ----
<S>                         <C>        <C>        <C>        <C>        <C>   
Non-accrual loans           $2,154     $3,417     $4,123     $2,772     $2,598

Accruing loans past
   due 90 days or more      $1,357     $1,537     $1,709     $1,543     $  561

Restructured loans          $  322     $  333     $    0     $    0     $    0

Other Real Estate owned     $1,531     $  258     $  256     $    0     $    0
</TABLE>

                                       -9-
<PAGE>   10
BUSINESS--CONTINUED

Summary of Loan Loss Experience
-------------------------------

This table summarized the Company's loan loss experience for each of the five
years ended December 31 (000s)

<TABLE>
<CAPTION>
                                1998          1997          1996         1995         1994
                                ----          ----          ----         ----         ----
<S>                           <C>          <C>           <C>           <C>          <C>   
Balance at Jan. 1:            $6,254       $ 6,827       $ 5,336       $5,101       $4,364
Acquired Allowance                 0             0          1285            0            0

Charge-offs
             Commercial          705         1,000          1091          248          144
             Real Estate         284             6             4            0           15
             Consumer          1,117         1,182           868          829          573
                              ------       -------       -------       ------       ------
                               2,106         2,188          1963        1,077          732


Recoveries
             Commercial          834            64            55           97          411
             Real Estate          66            19             0            0            0
             Consumer            295           232           239          265          214
                              ------       -------       -------       ------       ------
                               1,195           315           294          362          625
                              ------       -------       -------       ------       ------

Net Charge-offs                 (911)       (1,873)       (1,669)        (715)        (107)

Provision for loan losses      1,540         1,300          1875          950          844
                              ------       -------       -------       ------       ------

Balance at Dec. 31:            6,883       $ 6,254       $ 6,827       $5,336       $5,101
                               =====       =======       =======       ======       ======


Net Charge offs
to average loans                0.16%         0.34%         0.39%        0.18%        0.03%
</TABLE>

                                      -10-
<PAGE>   11
BUSINESS--CONTINUED

Allowance for Loan Losses
-------------------------

The allowance for loan losses is established through charges to operations by a
provision for loan losses. Loans which are determined to be uncollectible are
charged against the allowance and subsequent recoveries, if any, are credited to
the allowance. The amount charged to operations is based on several factors.
These include the following:

        1.      Analytical reviews of the loan loss experience in relationship
                to outstanding loans to determine an adequate allowance for loan
                losses required for loans at risk.

        2.      A continuing review of problem or at risk loans and the overall
                portfolio quality.

        3.      Regular examinations and appraisals of the loan portfolio
                conducted by the Bank's examination staff and the banking
                supervisory authorities.

        4.      Management's judgement with respect to the current and expected
                economic conditions and their impact on the existing loan
                portfolio.

The amount provided for loan losses exceeded actual net charge-offs by $629,000
in 1998 and $206,000 in 1996. Net charge-offs exceeded the amount provided for
loan losses by $573,000 in 1997.

It is management's practice to review the allowance on a quarterly basis to
determine whether additional provisions should be made after considering the
factors noted above. Based on these procedures, management is of the opinion
that the allowance at December 31, 1998 of $6,883,000 is adequate.

                                      -11-
<PAGE>   12
BUSINESS--CONTINUED

This table shows allocation of the allowance for loan losses as of the end of
the last five years. (000s)

<TABLE>
<CAPTION>
                                  12-31-98             12-31-97             12-31-96             12-31-95             12-31-94
                             -------------------  -------------------  -------------------  -------------------  -------------------
                                     Percent of           Percent of           Percent of           Percent of           Percent of
                                     Loans to             Loans to             Loans to             Loans to             Loans to
                             Amount  Total Loans  Amount  Total Loans  Amount  Total Loans  Amount  Total Loans  Amount  Total Loans
                             ------  -----------  ------  -----------  ------  -----------  ------  -----------  ------  -----------
<S>                          <C>     <C>          <C>     <C>          <C>     <C>          <C>     <C>          <C>     <C>
Commercial and Agriculture   $1,941      46%      $1,757       45%     $1,730      39%      $1,075      43%      $1,683       42%

Real Estate                   1,233      41%         331       40%         24      44%          52      33%          52       33%

Consumer                        778      13%         816       15%        826      17%         771      24%         588       25%

Additional Reserve Allocated
for current loans               835                  757                2,057                1,178                1,280

Unallocated                   2,096                2,593                2,190                2,260                1,498
                             ------               ------               ------               ------               ------
                             $6,883     100%      $6,254      100%     $6,827     100%      $5,336     100%      $5,101      100%
                             ======     ===       ======      ===      ======     ===       ======     ===       ======      === 
</TABLE>

                                      -12-
<PAGE>   13
BUSINESS--CONTINUED

Deposits
--------

Maturities of time certificates of deposits and other time deposits of $100,000
or more, outstanding at December 31, are summarized as follows: (000s)

<TABLE>
<CAPTION>
                                                         1998             1997
                                                         ----             ----
<S>                                                   <C>              <C>    
        Three months or less                          $11,370          $11,269
        Over three months through twelve months        25,855           18,380
        Over one year thru five years                   7,569           12,096
                                                      -------          -------
                                                      $44,794          $41,745
                                                      =======          =======
</TABLE>

Return on Equity and Assets

The following table shows consolidated operating and capital ratios of the
company for each of the last three years:

<TABLE>
<CAPTION>
                                                     Year Ended December 31

For the Years                                    1998         1997        1996
-------------                                    ----         ----        ----
<S>                                             <C>          <C>         <C>
Return on Assets (A)                             1.85%        1.75%       1.92%

Return on Equity (B)                            13.69%       13.92%      14.18%

Dividend Payout Ratio (C)                       38.67%       37.24%      36.49%

Equity to Assets Ratio (D)                      13.58%       12.55%      13.52%
</TABLE>

-------------------

        (A)     net income divided by average total assets
        (B)     net income divided by average equity
        (C)     dividends declared per share divided by net income per share
        (D)     average equity divided by average total assets

                                      -13-
<PAGE>   14
BUSINESS--CONTINUED

Loan Commitments and Standby Letters of Credit
----------------------------------------------

Loan commitments are made to accommodate the financial needs of our customers.
Letters of credit commit the Company to make payments on behalf of customers
when specific future events occur.

Both arrangements have credit risk essentially the same as that involved in
extending loans to customers and are subject to the Company's normal credit
policies. Collateral (e.g., securities, receivables, inventory, equipment) is
obtained based on Management's credit assessment of the customer.

<TABLE>
<CAPTION>
Off-balance sheet items at December 31   (000s)

                                               1998                  1997
                                               ----                  ----
<S>                                         <C>                   <C>    
Unused Commitments

       Open end consumer lines              $47,958               $43,267
       Other unused commitments              94,035                81,231

        Letters of Credit                    $2,602                $2,072
</TABLE>

                                      -14-
<PAGE>   15
BUSINESS--CONTINUED

<TABLE>
                                               SECURITY NATIONAL "NEXT FOUR QUARTERS"
                                                     ASSET/LIABILITY MANAGEMENT
                                                     STATIC GAP ANALYSIS (000s)
<CAPTION>
                                             Immediately
                                             Adjustable       End of 3/99       End of 6/99       End of 9/99       End of 12/99
                                           Runoffs   Rate    Runoffs   Rate    Runoffs   Rate    Runoffs   Rate    Runoffs   Rate
                                           -------   ----    -------   ----    -------   ----    -------   ----    -------   ----
<S>                                        <C>       <C>     <C>       <C>     <C>      <C>      <C>       <C>     <C>       <C>
Total Investment Securities                     51   5.44%    20,000   5.89%         0   0.00%    20,000   5.81%    10,275   5.70%
Total Short Term Investment                 17,850   4.40%         0   0.00%         0   0.00%         0   0.00%         0   0.00%
Net Loans                                   65,235   8.26%    34,426   8.91%    23,853   8.84%    19,457   8.91%    17,793   8.80%
Total Earning Assets                        83,136   7.43%    54,426   7.80%    23,853   8.84%    39,457   7.34%    28,068   7.67%
Total Non-Earning Assets                     1,285   9.17%         0   0.00%         0   0.00%         0   0.00%         0   0.00%
Total Assets                                84,420   7.46%    54,426   7.80%    23,853   8.84%    39,457   7.34%    28,068   7.67%
Total Noninterest Bearing Deposits               0   0.00%         0   0.00%         0   0.00%         0   0.00%         0   0.00%
Total Interest Bearing Deposits             39,836   4.38%    40,519   4.60%    53,956   4.71%    26,246   4.43%    18,197   3.72%
Total Deposits                              39,836   4.38%    40,519   4.60%    53,956   4.71%    26,246   4.43%    18,197   3.72%
Total Other Interest Bearing Liabilities    29,218   3.39%         0   0.00%         0   0.00%         0   0.00%         0   0.00%
Total Other Liabilities                          0   0.00%         0   0.00%         0   0.00%         0   0.00%         0   0.00%
Total Liabilities                           69,053   3.96%    40,519   4.60%    53,956   4.71%    26,246   4.43%    18,197   3.72%
Total Equity Capital                             0   0.00%         0   0.00%         0   0.00%         0   0.00%         0   0.00%
Total Liabilities and Capital               69,053   3.96%    40,519   4.60%    53,956   4.71%    26,246   4.43%    18,197   3.72%
Interval GAP                                15,367            13,906           (30,103)           13,212             9,871
Cumulative GAP                              15,367            29,273              (830)           12,382            22,253
Interval GAP/Total Assets                            2.71%             2.46%            (5.32%)            2.33%             1.74%
Cumulative GAP/Total Assets                          2.71%             5.17%            (0.15%)            2.19%             3.93%
Interval GAP:  Earning Assets                        2.57%             2.65%            (5.74%)            2.52%             1.88%
Cumulative GAP/Earning Assets                        2.57%             5.22%            (0.52%)            2.00%             3.88%
Interval Spread:  Earning Assets                     3.54%             3.20%             4.13%             2.91%             3.94%
Interval Spread:  Total Assets                       3.50%             3.20%             4.13%             2.91%             3.94%
</TABLE>

                                      -15-
<PAGE>   16
BUSINESS--CONTINUED

<TABLE>
                                               CITIZENS NATIONAL "NEXT FOUR QUARTERS"
                                                     ASSET/LIABILITY MANAGEMENT
                                                     STATIC GAP ANALYSIS (000s)
<CAPTION>
                                             Immediately
                                             Adjustable       End of 3/99       End of 6/99       End of 9/99        End of 12/99
                                           Runoffs   Rate    Runoffs   Rate    Runoffs   Rate    Runoffs   Rate    Runoffs    Rate
                                           -------   ----    -------   ----    -------   ----    -------   ----    -------    ----
<S>                                        <C>      <C>      <C>     <C>       <C>      <C>      <C>       <C>    <C>      <C>
Total Investment Securities                      0   0.00%     8,400   5.32%     3,500   5.78%     2,510   5.96%     1,107    5.03%
Total Short Term Investment                  2,500   4.90%     2,200   5.92%         0   0.00%         0   0.00%       500    5.13%
Net Loans                                   17,439   8.73%     2,361   8.50%     2,275   8.44%     9,321   8.18%     4,828   10.22%
Total Earning Assets                        19,939   8.25%    12,961   6.02%     5,775   6.83%    11,831   7.71%     6,435    8.93%
Total Non-Earning Assets                       578   8.14%         0   0.00%         0   0.00%         0   0.00%         0    0.00%
Total Assets                                20,518   8.24%    12,961   6.02%     5,775   6.83%    11,831   7.71%     6,435    8.93%
Total Noninterest Bearing Deposits               0   0.00%         0   0.00%         0   0.00%         0   0.00%         0    0.00%
Total Interest Bearing Deposits                120   5.18%    34,062   2.62%     8,690   4.77%     6,817   5.39%    33,344    3.07%
Total Deposits                                 120   5.18%    34,062   2.62%     8,690   4.77%     6,817   5.39%    33,344    3.07%
Total Other Interest Bearing Liabilities        17   4.52%       310   4.00%         0   0.00%         0   0.00%         0    0.00%
Total Other Liabilities                          0   0.00%         0   0.00%         0   0.00%         0   0.00%         0    0.00%
Total Liabilities                              137   5.10%    34,372   2.63%     8,690   4.77%     6,817   5.39%    33,344    3.07%
Total Equity Capital                             0   0.00%         0   0.00%         0   0.00%         0   0.00%         0    0.00%
Total Liabilities and Capital                  137   5.10%    34,372   2.63%     8,690   4.77%     6,817   5.39%    33,344    3.07%
Interval GAP                                20,381           (21,411)           (2,915)            5,014           (26,909)
Cumulative GAP                              20,381            (1,030)           (3,946)            1,068           (25,841)
Interval GAP/TotalAssets                            14.19%           (14.91%)           (2.03%)            3.49%            (18.74%)
Cumulative GAP/Total Assets                         14.19%            (0.72%)           (2.75%)            0.74%            (17.99%)
Interval GAP/Earning Assets                         15.51%           (16.80%)           (2.29%)            0.36%            (21.11%)
Cumulative GAP/Earning Assets                       15.51%            (1.29%)           (3.57%)            2.32%            (20.75%)
Interval Spread: Earning Assets                      3.16%             3.39%             2.06%             0.36%              5.86%
Interval Spread: Total Assets                        3.14%             3.39%             2.06%             2.32%              5.86%
</TABLE>

                                      -16-
<PAGE>   17
BUSINESS--CONTINUED

<TABLE>
                                                 THIRD SAVINGS "NEXT FOUR QUARTERS"
                                                     ASSET/LIABILITY MANAGEMENT
                                                     STATIC GAP ANALYSIS (000s)
<CAPTION>
                                             Immediately
                                             Adjustable       End of 3/99       End of 6/99       End of 9/99        End of 12/99
                                           Runoffs   Rate    Runoffs   Rate    Runoffs   Rate    Runoffs   Rate    Runoffs    Rate
                                           -------   ----    -------   ----    -------   ----    -------   ----    -------    ----
<S>                                        <C>      <C>      <C>      <C>      <C>      <C>      <C>      <C>      <C>       <C>
Total Investment Securities                  1,346   6.83%         0   0.00%    1,001    6.11%         0   0.00%         0    0.00%
Total Short Term Investment                  1,000   4.55%         0   0.00%        0    0.00%         0   0.00%         0    0.00%
Net Loans                                   18,554   8.78%    13,303   8.76%   12,465    8.08%    10,121   8.27%     8,771    7.98%
Total Earning Assets                        20,900   8.45%    13,303   8.76%   13,466    7.94%    10,121   8.27%     8,771    7.98%
Total Non-Earning Assets                       290   9.30%         0   0.00%        0    0.00%         0   0.00%         0    0.00%
Total Assets                                21,190   8.47%    13,303   8.76%   13,466    7.94%    10,121   8.27%     8,771    7.98%
Total Noninterest Bearing Deposits               0   0.00%     2,919   0.00%        0    0.00%         0   0.00%         0    0.00%
Total Interest Bearing Deposits              2,010   4.75%    11,496   5.37%   16,784    5.48%    18,845   5.43%    12,767    5.04%
Total Deposits                               2,010   4.75%    14,415   4.29%   16,784    5.48%    18,845   5.43%    12,767    5.04%
Total Other Interest Bearing Liabilities         0   0.00%         0   0.00%        0    0.00%         0   0.00%         0    0.00%
Total Other Liabilities                          0   0.00%         0   0.00%        0    0.00%         0   0.00%         0    0.00%
Total Liabilities                            2,010   4.75%    14,415   4.29%   16,784    5.48%    18,845   5.43%    12,767    5.04%
Total Equity Capital                             0   0.00%         0   0.00%        0    0.00%         0   0.00%         0    0.00%
Total Liabilities and Capital                2,010   4.75%    14,415   4.29%   16,784    5.48%    18,845   5.43%    12,767    5.04%
Interval GAP                                19,181            (1,112)          (3,318)            (8,725)           (3,997)
Cumulative GAP                              19,181            18,068           14,750              6,026             2,029
Interval GAP/Total Assets                           11.09%            (0.64%)           (1.92%)           (5.04%)            (2.31%)
Cumulative GAP/Total Assets                         11.09%            10.45%             8.53%             3.48%              1.17%
Interval GAP/Earning Assets                         12.29%             1.18%            (2.16%)           (5.68%)            (2.60%)
Cumulative GAP/Earning Assets                       12.29%            13.46%            11.31%             5.63%              3.03%
Interval Spread: Earning Assets                      3.70%             3.39%             2.45%             2.84%              2.94%
Interval Spread: Total Assets                        3.72%             4.48%             2.45%             2.84%              2.94%
</TABLE>

                                      -17-
<PAGE>   18
ITEM 2.      PROPERTIES

        The Security Banc Corporation is headquartered in Springfield, Ohio at
        40 South Limestone Street. The subsidiaries of the Company have 24
        banking offices located in Ohio. The Company owns 22 of the offices and
        the other two are leased. Additional information is contained in the
        Notes to Consolidated Financial Statements, Part IV, Item 14.

                                      -18-
<PAGE>   19
ITEM 3.       LEGAL PROCEEDINGS

              Registrant and its subsidiaries are not a party to any material
              legal proceedings.

ITEM 4.       SUBMISSION OF MATTERS TO A VOTE OF SECURITY HOLDERS

        1.      To elect four directors of Class II to serve until the Annual
                Meeting of Shareholders in 2002 or in the case of each director
                until his successor is duly elected and qualified.

        2.      To transact such other business as may properly come before the
                Annual Meeting or any adjournments thereof.

PART II
ITEM 5.       MARKET FOR REGISTRANT'S COMMON EQUITY AND RELATED
              SHAREHOLDER MATTERS
              The common stock of the Corporation is traded on the
              over-the-counter market. Transfer agent and registrar is The
              Registrar and Transfer Co., 10 Commerce Drive, Cranford, NJ 07016.
              Common stock market prices and dividends are shown in the annual
              shareholders' report for the year ended December 31, 1998 and
              incorporated herein by reference.

ITEM 6.       SELECTED FINANCIAL DATA
              The information required by this item is incorporated herein by
              reference to the registrant's 1998 Annual Report to Shareholders
              attached to this filing as Exhibit "13".

ITEM 7.       MANAGEMENT'S DISCUSSION AN ANALYSIS OF FINANCIAL CONDITION AND
              RESULTS OF OPERATION
              The information required by this item is incorporated herein by
              reference to the registrant's 1998 Annual Report to Shareholders
              attached to this filing as Exhibit "13".

ITEM 8.       FINANCIAL STATEMENTS AND SUPPLEMENTARY DATA
              The information required by this item is incorporated herein by
              reference to the registrant's 1998 Annual Report to Shareholders
              attached to this filing as Exhibit "13".

ITEM 9.       CHANGES IN AND DISAGREEMENTS WITH ACCOUNTANTS ON ACCOUNTING AND
              FINANCIAL DISCLOSURE
              None

                                      -19-
<PAGE>   20
PART III

ITEM 10.     DIRECTORS AND EXECUTIVE OFFICERS OF THE REGISTRANT
        The information required by this item concerning Directors is
        incorporated herein by reference to the registrant's 1999 Proxy
        Statement.

Executive Officers
------------------

The name, age, and position of the Executive Officers of the Registrant as of
March, 1999 is listed below along with their business experience during the past
five years. Officers are appointed annually by the Board of Directors at the
meeting of Directors immediately following the Annual Meeting of Stockholders.

<TABLE>
<CAPTION>
Name, Age, Position                        Business Experience During Past Five Years
-------------------                        ------------------------------------------
<S>                                        <C>
        Executive Officers
        ------------------

        Harry O. Egger, 59                 Security National Bank and Trust Co.
        Chairman, President, CEO           President 1981 - 1996
                                           Chairman, CEO since 1-1-97

        J. William Stapleton, 46           Security National Bank and Trust Co.
        Executive Vice President/CFO       Vice President since 9-18-84
                                           Executive Vice President since 1-1-97

        William C. Fralick, 44             Security National Bank and Trust Co.
        Vice President                     Vice President since 12-31-84
                                           President since 1-1-97

        Glenda S. Greenwood, 43            Security National Bank and Trust Co.
        Vice President                     Director of Marketing since 12-29-80
                                           Vice President since 1-1-97

        Daniel M. O'Keefe, 54              Security National Bank and Trust Co.
        Vice President                     Vice President/Trust Officer since 1-80
</TABLE>

ITEM 11.     EXECUTIVE COMPENSATION
        The information required by this item is incorporated herein by
        reference to the registrant's 1999 Proxy Statement.

                                      -20-
<PAGE>   21
PART III

ITEM 12.     SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS ANDMANAGEMENT
        The information required by this item is incorporated herein by
        reference to the Registrant's 1999 Proxy Statement.

ITEM 13.     CERTAIN RELATIONSHIPS AND RELATED TRANSACTIONS
        The information required by this item is incorporated herein by
        reference to the Registrant's 1999 Proxy Statement.

PART IV

ITEM 14.     EXHIBITS, FINANCIAL STATEMENT SCHEDULES, AND REPORTS ON FORM 8-K.

     a)      Document filed as part of the report

             1.      FINANCIAL STATEMENTS

                     The following consolidated financial statements and report
                     of independent auditors of Security Banc Corporation,
                     included in the 1998 Annual Report to its shareholders for
                     the year ended December 31, 1998 are incorporated by
                     reference in Item 8.

                     Report of Independent Auditors

                     Consolidated Statement of Condition, December 31, 1998 and
                     1997

                     Consolidated Statement of Income for the Years Ending
                     December 31, 1998, 1997, and 1996

                     Consolidated Statement of Shareholders' Equity for the
                     Years Ending December 31, 1998, 1997, and 1996

                     Consolidated Statement of Cash Flows for the Years Ending
                     December 31, 1998, 1997, and 1996

                     Notes to Consolidated Financial Statements

                                      -21-
<PAGE>   22
PART IV

ITEM 14.     EXHIBITS, FINANCIAL STATEMENT SCHEDULES, AND REPORTS ON FORM 8-K
             (CONT'D)

      a)     Document filed as part of the report

             2.      Schedules to the consolidated financial statements
                     required by Article 9 of Regulation S-X are not required
                     under the related instructions or are inapplicable, and
                     therefore have been omitted.

     (b)     Reports on Form 8-K - None


     (c)     Exhibits

             13 - Security Banc Corporation 1998 Annual Report

             23 - Consent of Independent Auditors

             27 - Financial Data Schedule

     (d)     Financial Statement Schedules - None

     Security Banc Corp. has the following subsidiaries:

             1.   Security National Bank and Trust Co.
             2.   Citizens National Bank
             3.   Third Savings and Loan Company

                                      -22-
<PAGE>   23
SIGNATURES

Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange
Act of 1934, the Registrant has duly caused this report to be signed on its
behalf by the undersigned, thereunto duly authorized.

                                  SECURITY BANC
            ---------------------------------------------------------
                            CORPORATION (Registrant)


By /s/ Harry O. Egger
  -----------------------------------------
Harry O. Egger, Chairman of the Board and Director
(Principal Executive Officer)


Pursuant to the requirements of the Securities Exchange Act of 1934, this report
has been signed below by the following persons on behalf of the registrant and
in the capacities and on the dates indicated.

<TABLE>
<S>                                               <C>
/s/ Larry E. Kaffenbarger                         /s/ Vincent J. Demana
----------------------------------------          ----------------------------------------
Director, Larry E. Kaffenbarger, 3-16-99          Director, Vincent J. Demana, 3-16-99


/s/ Chet L. Walthall                              /s/ Robert A. Warren
----------------------------------------          ----------------------------------------
Director, Chet L. Walthall, 3-16-99               Director, Robert A. Warren, 3-16-99


/s/ Larry D. Ewald                                /s/ Richard E. Kramer
----------------------------------------          ----------------------------------------
Director, Larry D. Ewald, 3-16-99                 Director, Richard E. Kramer, 3-16-99


/s/ Karen E. Nagle                                /s/ James R. Wilson
----------------------------------------          ----------------------------------------
Director, Karen E. Nagle, 3-16-99                 Director, James R. Wilson, 3-16-99


/s/ Thomas J. Veskauf                             /s/ Scott A. Gabriel
----------------------------------------          ----------------------------------------
Director, Thomas J. Veskauf, 3-16-99              Director, Scott A. Gabriel, 3-16-99


/s/ Harry O. Egger                                /s/ J. William Stapleton
----------------------------------------          ----------------------------------------
Chairman of the Board, President and CEO          Executive Vice President and
Harry O. Egger, 3-16-99                           Chief Financial Officer
                                                  (Principal Financial Officer)
                                                  J. William Stapleton, 3-16-99
/s/ Thomas L. Miller
----------------------------------------
Vice President/Controller Security
National Bank
Thomas L. Miller, 3-16-99
</TABLE>

                                      -23-