<PAGE>   1
                                  10-K/A NO. 1
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                         ------------------------------

                       AMENDMENT TO APPLICATION OR REPORT
                  FILED PURSUANT TO SECTION 12, 13 OR 15 (d) OF
                       THE SECURITIES EXCHANGE ACT OF 1934


                            SECURITY BANC CORPORATION
               (EXACT NAME OF REGISTRANT AS SPECIFIED IN CHARTER)

The undersigned registrant hereby amends the following items, financial
statements, exhibits or other portions of its Annual Report on Form 10-K for the
year ended December 31, 1999, as set forth in the pages attached hereto:

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

The following financial statement with respect to the Security Banc Corporation
401(k) Profit Sharing Savings Plan (the "Plan") are filed herewith as Exhibit
28.1, pursuant to Rule 15d-21 under the Securities Exchange Act of 1934, in lieu
of a filing on Form 11-K:

         (a)      Report of Independent Auditors

         (b)      Statements of Assets Available for Distribution to Plan
                  Participants-December 31, 1999 and 1998

         (c)      Statements of Changes in Assets Available for Distribution to
                  Plan Participants - years ended December 31, 1999 and 1998

         (d)      Notes to Financial Statements

         (e)      Schedule of Assets Held for Investment - December 31, 1999

         (f)      Schedule of Transactions or Series of Transactions in Excess
                  of 5% of the current value of Plan Assets - year ended
                  December 31, 1999

The Plan is subject to the Employee Retirement Income Security Act of 1974, as
amended, and the foregoing financial statements are filed in lieu of the
financial statements required by Items 1, 2, and 3 of Form 11-K.

The Consent of the Plan's independent auditors to the inclusion of the foregoing
financial statements herein and to the incorporation by reference of such
financial statements in the registrant's Registration Statement on Form S-8
pertaining to the Plan is attached as Exhibit 24.1.

Pursuant to the requirements of the Securities Exchange Act of 1934, the
registrant has duly caused this amendment to be signed on its behalf by the
undersigned, thereunto duly authorized.

SECURITY BANC CORPORATION



By /s/ Thomas L. Miller                               Date: June 7, 2000
   --------------------                                    -------------
   Thomas L. Miller
   Vice President/Controller
<PAGE>   2
                              Financial Statements
                         and Other Financial Information

                        Security Banc Corporation 401 (k)
                           Profit Sharing Savings Plan

                     Years ended December 31, 1999 and 1998
                       with Report of Independent Auditors

<PAGE>   3
                        Security Banc Corporation 401 (k)
                           Profit Sharing Savings Plan

                              Financial Statements
                         and Other Financial Information


                     Years ended December 31, 1999 and 1998




                                    CONTENTS

Report of Independent Auditors.................................................1

Audited Financial Statements

Statements of Net Assets Available for Benefits................................2
Statements of Changes in Net Assets Available for Benefits.....................3
Notes to Financial Statements..................................................4


Supplemental Schedule

Schedule of Assets Held for Investment Purposes At End of Year................10

<PAGE>   4
                         Report of Independent Auditors

Plan Committee
Security Banc Corporation
401(k) Profit Sharing Savings Plan

We have audited the accompanying statements of net assets available for benefits
of the Security Banc Corporation 401(k) Profit Sharing Savings Plan (the Plan)
as of December 31, 1999 and 1998, and for the related statements of changes in
net assets available for benefits for the years then ended. These financial
statements are the responsibility of the Plan's management. Our responsibility
is to express an opinion on these financial statements based on our audits.

We conducted our audits in accordance with auditing standards generally accepted
in the United States. These standards require that we plan and perform the audit
to obtain reasonable assurance about whether the financial statements are free
of material misstatement. An audit includes examining, on a test basis, evidence
supporting the amounts and disclosures in the financial statements. An audit
also includes assessing the accounting principles used and significant estimates
made by management, as well as evaluating the overall financial statement
presentation. We believe that our audits provide a reasonable basis for our
opinion.

In our opinion, the financial statements referred to above present fairly, in
all material respects, the net assets available for benefits of the Plan at
December 31, 1999 and 1998, and the changes in the net assets available for
benefits for the years then ended, in conformity with accounting principles
generally accepted in the United States.

Our audits were performed for the purpose of forming an opinion on the financial
statements taken as a whole. The accompanying supplemental schedule of assets
held for investment purposes at end of year as of December 31, 1999 is presented
for purposes of additional analysis, and is not a required part of the financial
statements but is supplementary information required by the Department of
Labor's Rules and Regulations for Reporting and Disclosure under the Employee
Retirement Income Security Act of 1974. The supplemental schedule is the
responsibility of the Plan's management. The supplemental schedule has been
subjected to the auditing procedures applied in our audits of the financial
statements and, in our opinion, is fairly stated in all material respects in
relation to the financial statements taken as a whole.

                                                  /s/ Ernst & Young LLP

Columbus, Ohio
May 11, 2000

                                                                               1
<PAGE>   5
                         Security Banc Corporation 401K
                          Profit Sharing Savings Plan

                Statements of Net Assets Available for Benefits

<TABLE>
<CAPTION>
                                                            DECEMBER 31
                                                      1999               1998
                                                  ------------------------------
<S>                                               <C>                <C>
ASSETS
Investments, at fair value                        $15,145,097        $18,914,407

Contribution receivable                                 4,627             31,128
Accrued interest and dividends                            218              2,455
                                                  ------------------------------

Total assets                                       15,149,942         18,947,990

LIABILITIES
Cash overdraft                                          1,781                 --
                                                  ------------------------------

Net assets available for benefits                 $15,148,161        $18,947,990
                                                  ==============================
</TABLE>

See accompanying notes.

                                                                               2
<PAGE>   6
                         Security Banc Corporation 401K
                          Profit Sharing Savings Plan

          Statements of Chanages in Net Assets Available for Benefits

<TABLE>
<CAPTION>
                                                               YEAR ENDED DECEMBER 31
                                                               1999              1998
                                                            -----------------------------
<S>                                                         <C>               <C>
Additions:
    Investment income:
      Interest and dividends                                $   479,995       $   303,660
      Net realized and unrealized appreciation
        in fair value of investments                         (4,771,312)        6,347,124
                                                            -----------       -----------
                                                             (4,291,317)        6,650,784
Contributions:
    Employer                                                    204,553           202,438
    Employee                                                    811,772           697,488
                                                            -----------       -----------

Total contributions                                           1,016,325           899,926

Deductions:
    Benefit payments                                            524,837           582,485
                                                            -----------       -----------

Net increase                                                 (3,799,829)        6,968,225

Net assets available for benefits, at beginning of year      18,947,990        11,979,765
                                                            -----------       -----------
Net assets available for benefits, at end of year           $15,148,161       $18,947,990
                                                            ===========       ===========
</TABLE>
See accompanying notes.

                                                                               3
<PAGE>   7
                        Security Banc Corporation 401 (k)
                           Profit Sharing Savings Plan

                          Notes to Financial Statements

                           December 31, 1999 and 1998

1. SIGNIFICANT ACCOUNTING POLICIES

BASIS OF ACCOUNTING

The financial statements of the plan are prepared on the accrual basis.

USE OF ESTIMATES

The preparation of financial statements in conformity with generally accepted
accounting principles requires management to make estimates and assumptions that
affect the amounts reported in the financial statements and accompanying notes.
Actual results could differ from those estimates.

RECLASSIFICATION

Certain amounts in the 1998 financial statements have been reclassified to
conform to the 1999 presentations.

VALUATION OF INVESTMENTS AND INCOME RECOGNITION

Marketable securities are stated at fair value. Securities traded on a national
securities exchange are valued at the last reported sales price on the last
business day of the plan year. Investments not traded on the over-the-counter
market and listed securities for which no sale was reported on that date are
valued at the average of the last reported bid and ask prices. Short-term
investment funds are stated at redemption value, which is equal to market value.

Purchases and sales of securities are recorded on a trade-date basis. Interest
income is recorded on the accrual basis. Dividends are recorded on the
ex-dividend basis.

Unrealized gains and losses are differences between the fair value and cost
basis of investments. The cost basis of the investments is using the average
cost method.

2. DESCRIPTION OF THE PLAN

The following description of the Security Banc Corporation 401(k) Profit Sharing
Savings Plan (the Plan) provides only general information. Participants should
refer to the summary plan description for a more complete description of the
Plan's provisions.

                                                                               4
<PAGE>   8

                        Security Banc Corporation 401 (k)
                           Profit Sharing Savings Plan

                    Notes to Financial Statements (continued)


2. DESCRIPTION OF THE PLAN (CONTINUED)

GENERAL

The Plan is a defined contribution plan established on January 1, 1989, which
covers all employees of Security Banc Corporation (the Corporation) and its
subsidiaries, meeting specified age requirements and following the completion of
one year of credited service (500 hours). The Plan is subject to the provision
of the Employee Retirement Income Security Act of 1974 (ERISA).

CONTRIBUTIONS

Participants are not required to make contributions to the Plan; however, they
may voluntarily contribute an amount not exceeding 15 percent of their pretax
compensation received while a participant during the year. Contributions are
also subject to the maximum allowed by Internal Revenue Service (IRS)
regulations. The Corporation has agreed to voluntarily contribute, each year out
of its net profits before deductions for federal income taxes, a percentage of
the matchable contributions made by each participant. The Corporation is
currently matching 50 percent of each participant's contributions up to the
first 6 percent of a participant's compensation.

PARTICIPANT ACCOUNTS

Each participant's account is credited with the participant's contributions,
Corporation's contributions and allocation of earnings or losses. Earnings or
losses of the trust fund are allocated quarterly among participants in the
proportion that each participant's account balance bears to the total value of
all participants' account balances. The Corporation pays all expenses of
administering the Plan.

                                                                               5
<PAGE>   9

                        Security Banc Corporation 401 (k)
                           Profit Sharing Savings Plan

                    Notes to Financial Statements (continued)


2. DESCRIPTION OF THE PLAN (CONTINUED)

VESTING

Participants are immediately vested in their contributions plus actual earnings
thereon. Vesting in the remainder of their accounts is based on years of
continuous service. A participant vests 20 percent per year of credited service
for five years and is 100 percent vested after five years of credited service.
Forfeitures will be used to reduce future Corporation matching contributions or
will be allocated to the separate account of each participant.

TERMINATION OF PLAN

Although the Corporation has not expressed any intent to do so, the Corporation
has the right under the Plan to discontinue contributions at any time and
terminate the Plan. In the event of termination of the Plan, distribution would
be made to participants in the amount of their respective account balances.
Under the Plan, all contributions and earnings thereon are immediately vested
and fully nonforfeitable.

PAYMENT OF BENEFITS

On termination of service, a participant may receive a lump-sum amount equal to
the vested value of his or her account, or upon death, disability or retirement,
elect to receive annual installments over a period not to exceed fifteen years.

3. INVESTMENT OPTIONS

Plan participants may allocate their accounts between funds based on an election
filed at the start of the quarter after the employee becomes eligible to
participate in the Plan. Participants may change their allocation at any time.

The Plan provides for nine separate investment programs with separate funds.

PNC Temp Fund - The fund seeks to obtain a high level of current income as is
consistent with the preservation of principal and liquidity within the standards
of the Portfolio.

                                                                               6
<PAGE>   10
                        Security Banc Corporation 401 (k)
                           Profit Sharing Savings Plan

                    Notes to Financial Statements (continued)


3. INVESTMENT OPTIONS (CONTINUED)

Vanguard Wellington Fund - The fund seeks to obtain as much income as possible,
consistent with preservation of capital, by investing in a broadly diversified
portfolio of high yielding securities, including common stocks, preferred
stocks, and bonds.

Banc Corporation Stock Fund - The fund provides a means to invest in shares of
Security Banc Corporation's Common Stock, $1.5625 par value. Security Banc
Corporation is the parent company of Security National Bank, Citizens National
Bank, and Third Savings and Loan.

Security Investment Account II - The fund is the bank money market fund.

Federated Government Ultrashort Institutional Fund - The fund seeks a high rate
of income through investment in high and upper-medium grade fixed-income
obligations.

Fidelity Magellan Fund - The fund seeks capital appreciation by investing
primarily in common stock and securities convertible into common stock that
offer potential for growth.

Janus Worldwide Fund - The fund seeks capital growth through investments in
foreign securities.

Franklin Small Cap Growth Fund - The fund seeks long-term capital appreciation
by investing primarily in common stocks of small and medium-sized companies and
securities convertible into common stock.

Vanguard Index Fund - The funds seeks investment results that correspond with
the price and yield performance of the S&P 500 index.

Fidelity Advisor Institutional Growth Opportunity Fund - The fund seeks capital
appreciation by investing primarily in common stocks and securities convertible
into common stock.

                                                                               7
<PAGE>   11
                        Security Banc Corporation 401 (k)
                           Profit Sharing Savings Plan

                    Notes to Financial Statements (continued)

4. INVESTMENTS

The Plan's trustee is Security National Bank and Trust Company, a wholly-owned
subsidiary of the Corporation. The following individual investments represent 5
percent or more of the fair value of assets available for benefits as of
December 31, 1999 and 1998:

<TABLE>
<CAPTION>
                                                            DECEMBER 31
                                                       1999             1998
                                                    ----------------------------
<S>                                                 <C>              <C>
Security Banc Corporation Common Stock              $9,156,753       $14,557,514
Vanguard Index Fund                                  1,644,750         1,334,219
PNC Temp Fund                                          868,246                --
Fidelity Magellan Fund                                 936,653                --
</TABLE>

The Plan's investments (including investments bought, sold, and held during the
year) appreciated (depreciated) in carrying value as follows:

<TABLE>
<CAPTION>
                                                     YEAR ENDED DECEMBER 31
                                                    1999                 1998
                                                --------------------------------
<S>                                             <C>                   <C>
Equity Mutual Funds                             $   771,384           $  559,258
Common Stock                                     (5,540,957)           5,786,075
Fixed Income Mutual Fund                             (1,739)               1,791
                                                --------------------------------
Total                                           $(4,771,312)          $6,347,124
                                                ================================
</TABLE>

5. INCOME TAX STATUS

The Plan has received a determination letter from the Internal Revenue Service
dated June 17, 1998, stating that the Plan is qualified under Section 401(a) of
the Internal Revenue Code (IRC) and, therefore, the related trust is exempt from
taxation. Once qualified, the Plan is required to operate in conformity with IRC
to maintain its qualification. The Plan Administrator believes the Plan is being
operated in compliance with the applicable requirements of IRC and, therefore,
believes that the Plan is qualified and the related trust is tax exempt.

                                                                               8
<PAGE>   12
                        Security Banc Corporation 401 (k)
                           Profit Sharing Savings Plan

                    Notes to Financial Statements (continued)

6. TRANSACTIONS WITH PARTIES-IN-INTEREST

The Plan is assessed a quarterly trust service fee by the Trust Company based on
the market value of Plan assets held in trust. These fees are paid by the
Corporation on behalf of the Plan. Annual fees incurred were $20,771 and $20,480
in 1999 and 1998, respectively.

7. TERMINATED PARTICIPANTS

Included in net assets available for benefits are amounts allocated to
individuals who have withdrawn from the Plan. Amounts allocated to these
participants were $55,365 at December 31, 1999.

                                                                               9
<PAGE>   13
                        SECURITY BANC CORPORATION 401 (K)
                           PROFIT SHARING SAVINGS PLAN

         SCHEDULE OF ASSETS HELD FOR INVESTMENT PURPOSES AT END OF YEAR

                                December 31, 1999

                                                                EIN#: 31-0389990
                                                                     Plan #: 002

<TABLE>
<CAPTION>
                                                                                    FAIR
                 DESCRIPTION                           SHARES         COST          VALUE
--------------------------------------------------------------------------------------------
<S>                                                     <C>        <C>           <C>
Fidelity Advisor Institutional Growth Opportunity
   Fund                                                 14,612     $  598,382    $   680,189
Federated Government Ultrashort Institutional Fund
                                                        77,311        154,656        153,075
Vanguard Wellington Fund                                21,609        652,267        604,189
Janus Worldwide Fund                                     4,880        213,769        373,011
Fidelity Magellan Fund                                   6,855        665,307        936,653
Franklin Small Cap Growth Fund                          16,390        311,833        723,295
PNC Temp Fund                                          866,117        866,117        866,117
Security Investment Account II                           7,065          7,065          7,065
Security Banc Corporation Common Stock*                321,290      5,014,638      9,156,753
Vanguard Index Fund                                     12,154      1,114,132      1,644,750
                                                                   -------------------------
Total assets held for investment                                   $9,598,166    $15,145,097
                                                                   =========================
</TABLE>

* Party in interest to the plan.

                                                                              10