<PAGE>   1
                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION

                             Washington, D.C. 20549

                                    FORM 10-K

                     ANNUAL REPORT UNDER SECTION 13 OR 15(d)
                     OF THE SECURITIES EXCHANGE ACT OF 1934

     For the Fiscal Year Ended Dec. 31, 1997 Commission File Number 0-14773

                         NATIONAL BANCSHARES CORPORATION

                   Ohio                               34-1518564
          State of incorporation                      I.R.S. Employer
                                                      Identification No.

                  112 West Market Street, Orrville, Ohio 44667
                     Address of principal executive offices

Registrant's telephone number: (330) 682-1010

Securities registered pursuant to Section 12(b) of the Act:  None

Securities registered pursuant to section 12(g) of the Act:

                         Common Stock, $10.00 Par Value
                                 Title of Class

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 (or for such shorter period that the registrant was
required to file such reports), 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 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. __X__

State the aggregate market value of the voting stock held by non-affiliates of
the registrant as of March 4, 1998: $54,518,658.

Indicate the number of shares outstanding of each of the registrant's classes of
common stock, as of March 4, 1998.
                    Common Stock, $10.00 Par Value: 1,141,752

Documents Incorporated by Reference:

- Portions of the registrant's Proxy Statement dated March 23,1998 and
previously filed March 18, 1998, are incorporated by reference into Part III. 
- Portions of the registrant's Annual Report to Shareholders, December 31, 1997
are incorporated by reference in Parts I, II, IV.



PAGE 1
<PAGE>   2



<TABLE>
<CAPTION>
Form 10-K Cross Reference Index                                        Page
<S>                                                                    <C>
  Part I
    Item 1 - Business
      Description of Business                                          4
      Financial Ratios - Note 1                                        A23
      Daily Average Balance Sheets, Interest and Rates - Note 1        A22
      Volume and Rate Variance Analysis                                5
      Investment Portfolio                                             7
      Loan Portfolio                                                   8
      Summary of Loan Loss Experience                                  9
      Deposits                                                         10
    Item 2 - Properties                                                4
    Item 3 - Legal Proceedings                                         4
    Item 4 - Submission of Matters to a Vote of Security Holders  - None

  Part II
    Item 5 - Market for the Registrant's Common Equity
             and Related Stockholder Matters - Note 1                  A9
    Item 6 - Selected Financial Data - Note 1                          A1
    Item 7 - Management's Discussion and Analysis of Financial
             Condition and Results of Operation - Note 1               A2-8
    Item 7A - Quantitative and Qualitative Disclosures About
             Market Risk                                               6-7
    Item 8 - Financial Statements - Note 1                             A10-21
    Item 9 - Changes in and Disagreements with Accountants on 
             Accounting and Financial Disclosure - None

  Part III
    Item 10- Directors of the Registrant - Note 2                      B3
             Executive Officers of the Registrant                      4
    Item 11- Executive Compensation - Note 2                           B5
    Item 12- Security Ownership of Certain Beneficial
             Owners and Management - Note 2                            B3
    Item 13- Certain Relationships and Related Transactions - Note 2   B7

  Part IV
    Item 14- Exhibits, Financial Statement Schedules and Reports on Form 8-K
      Report of Deloitte & Touche L.L.P., Independent Auditors         A21
      Financial Statements: - Note 1
        Consolidated Balance Sheets as of December 31,
          1997 and 1996                                                A10
        Consolidated Statements of Income for the Years Ended
          December 31, 1997, 1996 and 1995                             A11
        Consolidated Statements of Cash Flows for the Years
          Ended December 31, 1997, 1996 and 1995                       A13
        Consolidated Statements of Changes in Stockholders'
          Equity for the Years Ended December 31, 1997,
          1996 and 1995                                                A12
        Notes to Financial Statements - Note 1                         A14-21
      Reports on Form 8-K filed in fourth quarter of 1997: None
      Exhibit Table                                                    13
  Signatures                                                           11-12

Appendix A - National Bancshares 1997 Annual Report to                 A
                 Shareholders
</TABLE>




PAGE 2
<PAGE>   3


Note 1 - Incorporated by reference from the registrant's Annual Report to
         Shareholders for the year ended December 31, 1997 -- Appendix A

Note 2 - Incorporated by reference from the registrant's proxy
         statement dated March 23, 1998  previously filed with the SEC on 
         March 18, 1998


PAGE 3
<PAGE>   4

Item 1 - Business:
National Bancshares Corporation (the "Company"), incorporated in 1985, is a one
bank holding company for First National Bank, Orrville, Ohio (the "Bank"). The
formation was approved by shareholders on April 24, 1986 and consummated on June
2, 1986. The Bank offers a full line of services usually found in any commercial
bank operation, including checking accounts, savings accounts, certificates of
deposit, personal loans, loans to business and industry, installment loans,
safety deposit boxes and credit cards. The Bank does not have trust powers and,
therefore, does not offer trust services. The Bank operates nine full service
offices and one limited service office in a market area comprising most of Wayne
County, portions of western Stark County, northeastern Holmes County and
southern Medina County. There are approximately 17 other banking and thrift
organizations in the immediate market area. No major elimination of services
presently offered is anticipated in the immediate future.

The Bank is a member of the Federal Reserve System and its deposits are insured
by the Federal Deposit Insurance Corporation. It is subject to supervision,
examination and regulation by the Comptroller of the Currency. The Company is
also subject to supervision, examination and regulation by the Federal Reserve
System. Management is not currently aware of any regulatory recommendations
which if were to be implemented would have a material effect on the registrant.

Item 2 - Properties:
The headquarters of the Company and the Bank are located in Orrville, Ohio. The
Bank has a total of ten banking office buildings which are located in Orrville,
Dalton, Kidron, Smithville, Mt. Eaton, Apple Creek, Lodi and Seville, Ohio. All
buildings are owned by the Bank with the exception of the Seville Office which
is a leased facility.

Item 3 - Legal Proceedings
There were no legal proceedings other than ordinary routine litigation
incidental to business during 1997.

Item 10 - Executive Officers
The Executive Officers of the Company are as follows:

<TABLE>
<CAPTION>
Name                       Age      Position
<S>                        <C>      <C>
Charles J. Dolezal         45       President
                                    President of First National Bank

Kenneth R. VanSickle       50       Senior V.P., Secretary
                                    Senior V.P., Chief Loan Officer of
                                    First National Bank

Lawrence M. Cardinal, Jr.  46       Vice President, Treasurer
                                    Vice President & Controller of
                                    First National Bank
</TABLE>

There is no family relationship between any of the above executive officers. Mr.
Dolezal has been an executive officer of the Company since its formation in 1986
and the Bank during the past 5 years. Mr. VanSickle was appointed Senior V.P.,
Secretary of the Company on April 24, 1997 and has been an executive officer of
the Bank during the past 5 years. Mr. Cardinal was appointed Vice President,
Treasurer of the Company and Vice President & Controller of the Bank on April
24, 1997. Mr. Cardinal previously worked as an audit manager for the CPA firm of
Reinhard, Kopko and Keller and as Senior Vice President and Controller for The
First National Bank of Ohio during the past 5 years.





PAGE 4
<PAGE>   5

VOLUME AND RATE VARIANCE ANALYSIS

The following table represents a summary analysis of changes in interest income,
interest expense and the resulting net interest income on a tax equivalent basis
for the periods presented each, as compared with the preceding period. Volume is
based on daily average balances.

<TABLE>
<CAPTION>
(Dollars in thousands)                  1997 versus 1996                   1996 versus 1995
                                      Increase (Decreases)               Increase (Decreases)
                                        Due to Changes In                  Due to Changes In
                                -------------------------------    ------------------------------

                                                        Net                               Net
                                     Volume      Rate   Change         Volume      Rate   Change
                                -------------------------------    ------------------------------
<S>                                     <C>      <C>       <C>         <C>       <C>      <C> 
Interest Income
 Investment securities:
  Taxable                               $71     ($56)      $15         ($591)    ($135)   ($726)
  Nontaxable                            181      (17)      164           (41)       (4)     (45)
  (tax equivalent basis)*
 Federal funds sold                      46       15        61           (15)      (47)     (62)
 Loans (including
  nonaccrual loans)                     310      (66)      244         1,090      (154)     936
                                -------------------------------    ------------------------------

   Total interest Income
   (tax equivalent basis)*             $608    ($124)     $484          $443     ($340)    $103
                                ===============================    ==============================


Interest Expense
 Deposits
  Interest bearing checking            ($18)    ($16)     ($34)         ($32)     ($42)    ($74)
  Savings                                24       (1)       23            11         6       17
  Time, $100,000
   and over                             160       (9)      151            27        44       71
  Time, other                            35      (13)       22           194         3      197
 Other funds purchased                   52       (2)       50          (106)       (7)    (113)
                                -------------------------------    ------------------------------

   Total interest
    expense                            $253     ($41)     $212           $94        $4      $98
                                ===============================    ==============================


Changes in net
 interest income (tax
 equivalent basis)*                    $355     ($83)     $272          $349     ($344)      $5
                                ===============================    ==============================

<FN>
* Tax equivalence based on highest statutory tax rates of 34%.
</TABLE>


PAGE 5
<PAGE>   6

QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK

The following table summarizes the repricing opportunities of interest bearing
assets and liabilities:

Gap Report
December 31, 1997
(Millions of dollars)
<TABLE>
<CAPTION>
                                 3 Months          6 Months          12 Months         1-5 Years          5+ Years
                               Period   Accum.   Period   Accum.   Period   Accum.   Period   Accum.     Period   Accum.
<S>                             <C>      <C>      <C>      <C>      <C>      <C>      <C>     <C>         <C>     <C>   
Rate sensitive assets:
 Fed funds sold                  $8.5     $8.5     $0.0     $8.5     $0.0     $8.5     $0.0     $8.5       $0.0     $8.5
 Securities                       3.5      3.5      4.2      7.7      2.7     10.4     33.2     43.6       38.1     81.7
 Net loans                       21.9     21.9     10.4     32.3     19.7     52.0     19.7     71.7        6.6     78.3
                             --------------------------------------------------------------------------------------------
TOTAL                           $33.9    $33.9    $14.6    $48.5    $22.4    $70.9    $52.9   $123.8      $44.7   $168.5
                             ============================================================================================

Rate sensitive
 liabilities:
  Checking (1)                  $29.6    $29.6     $0.0    $29.6     $0.0    $29.6     $0.0    $29.6       $0.0    $29.6
  Savings (2)                     0.0      0.0      0.0      0.0      0.0      0.0     42.2     42.2        0.0     42.2
  Time                           20.1     20.1      9.5     29.6      9.8     39.4     12.4     51.8        0.0     51.8
  Money market borrow             3.6      3.6      0.0      3.6      0.0      3.6      0.0      3.6        0.0      3.6
  TT&L note account               1.0      1.0      0.0      1.0      0.0      1.0      0.0      1.0        0.0      1.0
                             --------------------------------------------------------------------------------------------
TOTAL                           $54.3    $54.3     $9.5    $63.8     $9.8    $73.6    $54.6   $128.2       $0.0   $128.2
                             ============================================================================================


Rate sensitivity gap           -$20.4   -$20.4     $5.1   -$15.3    $12.6    -$2.7    -$1.7    -$4.4      $44.7    $40.3

Gap percentage                    62%      62%     154%      76%     229%      96%      97%      97%        NA      131%

Gap/total assets                 -11%     -11%       3%      -8%       7%      -1%      -1%      -2%        24%      22%

Gap/capital                      -78%     -78%      19%     -58%      48%     -10%      -6%     -17%       171%     154%

<FN>
(1) Checking includes NOW and MMDA
(2) Savings includes passbook and statement savings which do not have a preset
repricing date and have been included in the 1-5 years due to the relative
interest rate insensitivity.
</TABLE>

Management considers interest rate risk to be the Company's most significant
market risk. Management focuses on maintaining consistent growth in net interest
income, while managing interest rate risk within Board-approved policy limits.
The Company's Asset/Liability Management Committee, which consists of the
Company's Executive Officers and reports directly to the Board of Directors,
monitors and manages interest rate risk in order to maintain an acceptable level
of possible change in net interest income as a result of changes in interest
rates. The Company does not own any trading assets and is not subject to foreign
currency exchange or commodity price risk.

The Company uses a static gap analysis model as its primary method to identify
and manage its interest rate risk. The model measures the difference between the
assets and liabilities repricing or maturing within specific time periods. An
asset-sensitive position indicates that there are more rate-sensitive assets
than rate-sensitive liabilities repricing or maturing within specific time
horizons, which would generally imply a favorable impact on net interest income
in periods of rising interest rates and a negative impact in periods of falling
rates. A liability-sensitive position would generally imply a negative impact on
net interest income in periods of rising rates and a positive impact in periods
of falling rates.







PAGE 6
<PAGE>   7

QUANTITATIVE  AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK  (cont.)

Gap analysis has limitations because it cannot measure the effect of interest
rate movements and competitive pressures on the repricing and maturity
characteristics of interest-earning assets and interest-bearing liabilities. The
model assumes that certain assets and liabilities of similar maturity or
repricing opportunities will react the same to changes in interest rates.
However, certain types of financial instruments may react in advance to changes
in market rates, while other types of financial instruments may lag behind the
change in general market rates.

The estimated impact on the net interest margin from modestly rising or falling
interest would be relatively insignificant due to the short duration of mismatch
within the first 12 months. The following table shows the estimated change in
net interest income over 12 months if interest rates were to immediately
increase or decrease by 200 basis points.

<TABLE>
<CAPTION>
     Change in                                         Percentage Change in
     Interest Rates                                    Net Interest Income
     (basis points)                                      Over 12 Months
     ---------------------------------------------------------------------
          <S>                                                  <C> 
         +200                                                 -2.8%
         -200                                                  2.8%
</TABLE>

Management's goal is to manage the Company's interest rate risk by maintaining
the gap between interest-earning assets and interest-bearing liabilities
repricing in a one-year period within a range of plus or minus 10% of total
assets.




INVESTMENT PORTFOLIO

The carrying amounts and distribution of the Company's investment securities
held are summarized in the Annual Report to Shareholders (Appendix A, Page 15,
Note 3). The carrying amount, maturities and approximate weighted average yields
(on a tax equivalent basis) at December 31, 1997 are as follows:

INVESTMENT PORTFOLIO
December 31, 1997
(Dollars in thousands)
<TABLE>
<CAPTION>
                                 Total                 0 to 1 Year             1 to 5 Years           5 Years and Over
                          Amount       Yield       Amount       Yield       Amount       Yield      Amount       Yield
<S>                        <C>              <C>     <C>             <C>      <C>             <C>     <C>              <C> 
US Treasury                $  9,180         6.8%    $  3,011        6.1%     $  5,040        6.8%    $  1,129         8.5%
US Agencies                  30,099         6.8%       1,532        5.2%        9,899        6.7%      18,668         7.0%
State & political
 subdivisions                22,057         8.8%       1,092        8.8%        8,427        8.5%      12,538         8.9%
Other securities             20,448         6.5%       4,891        7.3%        9,819        6.8%       5,738         5.5%
                        ---------------------------------------------------------------------------------------------------
TOTAL                      $ 81,784         7.3%    $ 10,526        6.8%     $ 33,185        7.2%    $ 38,073         7.4%
                        ===================================================================================================
</TABLE>

$7.5 million of investment securities have a remaining maturity more than 10
years. There was no single issuer of securities where the total book value of
such securities exceeded 10% of shareholders' equity except for US government
obligations.




PAGE 7
<PAGE>   8

LOAN PORTFOLIO

The detail of the loan portfolio balances are included in the Annual Report to
Shareholders (Appendix A, Page 16, Note 4).

MATURITIES AND SENSITIVITIES OF LOANS TO CHANGES IN INTEREST RATES
The following are approximate maturities and sensitivity to changes in interest
rates of certain loans exclusive of real estate mortgages and consumer loans as
of December 31, 1997.

<TABLE>
<CAPTION>
Types of Loans                          0 to 1 Year    1 to 5 Years     5 and Over Years       Total
(Dollars in Thousands)
<S>                                         <C>                <C>                  <C>      <C>    
Commercial                                  $10,112            $732                          $10,844
Real Estate Construction                       $383          $1,030                 $505      $1,918

Above loans due beyond 1 year with:
Predetermined interest rates                                                                    $550
Adjustable interest rates                                                                     $1,717
</TABLE>

NONACCRUAL AND PAST DUE LOANS
Generally, recognition of interest income is discontinued where reasonable doubt
exists as to the collectability of the interest. Income from nonaccrual loans is
recorded when received. The difference between interest income recognized on
such loans and income that would have been recognized at original contractual
rates is immaterial. The bank generally places loans on a non-accrual status
when a default of principal or interest has existed for 90 days or more. The
bank generally does not renegotiate loans due to deterioration in the financial
position of the borrower. The amounts of renegotiated loans are not considered
material.

<TABLE>
<CAPTION>
(Dollars in Thousands)                 12/31/97    12/31/96
<S>                                        <C>         <C> 
90 Days Past Due and Accruing              $126        $458
Nonaccruing Loans                          $427         $85
</TABLE>

POTENTIAL LOAN PROBLEMS
Management reviews the loan portfolio for potential loan problems on a monthly
basis. The following loans were classified by management and include the above
nonaccrual and past due loan totals. The amount shown below is the outstanding
loan balance which has not been reduced by collateral values.

<TABLE>
<CAPTION>
(Dollars in Thousands)        12/31/97    12/31/96
<S>                             <C>         <C>   
Loss                                $6          $0
Doubtful                            54          95
Substandard                      1,420         930
OAEM                               660         742
Watch                                0           0
                           ------------------------
Total                           $2,140      $1,767
                           ========================
</TABLE>

LOAN CONCENTRATIONS
Due to the nature of our market area, it is management's opinion that there are
no significant loan concentrations of 10% of total loans to borrowers engaged in
similar activities other than noted in the loan categories disclosed in the
Annual Report to Shareholders (Appendix A, Page 16, Note 4).





PAGE 8
<PAGE>   9

SUMMARY OF LOAN LOSS EXPERIENCE
The determination of the balance of the allowance for loan losses historically
has been based on an overall analysis of the loan portfolio and reflects an
amount, which, in management's judgment, is adequate to provide for potential
loan losses. This analysis considers, among other things, the Company's loan
loss experience, present and potential risks of the loan portfolio and general
economic conditions. In addition, management considers the examinations of the
loan portfolio by federal regulatory agencies and internal reviews and
evaluations. The Company's allocation of the allowance for loan losses by
category represents only an estimate for each category of loans based upon a
detailed review of the loan portfolio by management.

Transactions in the allowance for loan losses are maintained by three major loan
categories and the summary of such transactions for periods indicated follows:

CHANGES IN ALLOWANCE
FOR LOAN LOSSES
<TABLE>
<CAPTION>
(Dollars in Thousands)                     1997           1996
<S>                                           <C>             <C>   
Balance at the beginning of period            $1,151          $1,046
Loans charged off:
 Commercial & industrial                          34              77
 Real estate                                      19               5
 Consumer                                         38              60
                                      -------------------------------
Total loans charged off                           91             142
                                      -------------------------------

Recoveries of loans charged off:
 Commercial & industrial                           1              43
 Real estate                                      30               0
 Consumer                                         21              24
                                      -------------------------------
Total recoveries                                  52              67
                                      -------------------------------
Net loans charged off                             39              75
                                      -------------------------------
Provision charged to
 operating expense                               120             180
                                      -------------------------------
Balance at end of period                      $1,232          $1,151
                                      ===============================

Net charge-offs to
 average loans                                  0.05            0.10
                                      ===============================
</TABLE>


DISTRIBUTION OF ALLOWANCE FOR
LOAN LOSSES BY CATEGORY
<TABLE>
<CAPTION>
(Dollars in thousands)                      December 31, 1997              December 31, 1996

                                                          % of                          % of
                                          Amount       Total Loans      Amount      Total Loans
<S>                                           <C>               <C>        <C>                <C> 
Commercial & industrial                          $91             16%          $74              17%
Real estate construction                           0              2%            0               2%
Real estate mortgages                             18             70%           18              67%
Consumer loans                                    11             12%           19              14%
Unallocated                                    1,112             N/A        1,040              N/A
                                      -------------------------------------------------------------
TOTAL                                         $1,232            100%       $1,151             100%
                                      =============================================================
</TABLE>






PAGE 9
<PAGE>   10

DEPOSITS

The classification of average deposits and the average rate paid on such
deposits for periods ending December 31, 1997, 1996 and 1995 is included in
Analysis of Net Interest Earnings included in the Annual Report to Shareholders
(Appendix A, Page 22).

 A summary of maturities of time deposits of $100,000 or more is as follows.

<TABLE>
<CAPTION>
                                                       12/31/97             12/31/96
<S>                                           <C>                  <C>              
Three months or less                          $      10,652,218    $       9,514,277
Over 3 months through 6 months                        1,018,351              218,945
Over 6 months through 12 months                         321,236              809,918
Over 12 months                                          729,535            1,026,845
                                           ------------------------------------------
                                              $      12,721,340    $      11,569,985
                                           ==========================================
</TABLE>




PAGE 10
<PAGE>   11

                                   SIGNATURES

Pursuant to the requirements 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.

                         NATIONAL BANCSHARES CORPORATION




DATE:             3-17-98           /s/ Charles J. Dolezal
         -----------------          --------------------------------
                                    Charles J. Dolezal, President


DATE:             3-17-98           /s/ Lawrence M. Cardinal, Jr.
         -----------------          --------------------------------
                                    Lawrence M. Cardinal, Jr., V.P.,Treasurer
                                    (Principal Financial Officer)

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


DATE:             3-17-98           /s/ Charles J. Dolezal
         -----------------          --------------------------------
                                    Charles J. Dolezal, Chairman


DATE:             3-17-98           /s/ Sara Balzarini
         -----------------          --------------------------------
                                    Sara Balzarini, Director


DATE:             3-17-98           /s/ James L. Gerber
         -----------------          --------------------------------
                                    James L. Gerber, Director


DATE:             3-17-98           /s/ Ray D. Gill
         -----------------          --------------------------------
                                    Ray D. Gill, Director


DATE:             3-17-98           /s/ John W. Kropf
         -----------------          --------------------------------
                                    John W. Kropf, Director


DATE:             3-17-98           /s/ Steve Schmid
         -----------------          --------------------------------
                                    Steve Schmid, Director



PAGE 11
<PAGE>   12

DATE:                3-17-98                 /s/ John E. Sprunger
               -----------------             --------------------------------
                                             John E. Sprunger, Director


DATE:                 3-17-98                /s/ James F. Woolley
              ------------------             --------------------------------
                                             James F. Woolley, Director


DATE:                 3-17-98                /s/Albert Yeagley
              ------------------             ---------------------------------
                                             Albert Yeagley, Director



PAGE 12
<PAGE>   13

EXHIBIT INDEX


<TABLE>
<CAPTION>
Exhibit No.                                                                     If incorporated by Reference,
Under Reg.          Form 10-K                                                   Documents with Which Exhibit
S-K, Item 601       Exhibit No.       Description of Exhibits                   was Previously Filed with SEC
<S>                 <C>               <C>                                       <C>
(3)(i)                                Amended Articles of Incorporation         Registration Statement S-4 filed
                                                                                3/31/86 File No. 33-03711
(3)(ii)                               Code of Regulations                       Registration Statement S-4 filed
                                                                                3/31/86 File No. 33-03711
(11)                A23               Computation of Earnings per Share         Incorporated by reference
(12)                A23               Computation of Ratios                     Incorporated by reference
(13)                A                 1997 Annual Report to Shareholders
(21)                A1                Subsidiaries of the registrant            Incorporated by reference
(23)                                  Consent of Deloitte & Touche, L.L.P.
(27)                                  Financial Data Schedule
</TABLE>

No other exhibits are required to be filed herewith pursuant to Item 601 of
Regulation S-K.

PAGE 13