<PAGE>   1
                                    FORM 10-Q


                    U.S. SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549


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


                     QUARTERLY REPORT PURSUANT TO SECTION 13
                     OF THE SECURITIES EXCHANGE ACT OF 1934
                       FOR THE QUARTER ENDED JUNE 30, 2000


                         FIRST NATIONAL BANCSHARES, INC.
             ------------------------------------------------------
             (exact name of registrant as specified in its charter)


           FLORIDA                                                 06-1522028
------------------------------                                ------------------
(Jurisdiction of Organization)                                  I.R.S. Employer
                                                              Identification No.


5817 MANATEE AVENUE WEST, BRADENTON, FLORIDA                          34209
--------------------------------------------                       ----------
      (Address of principal office)                                (Zip Code)


Registrant's telephone number, including area code: (941) 794-6969
                                                    --------------


Indicate by check mark whether the registrant (1) has filed all reports required
to be filed by Section 13 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 of
the past 90 days.


Yes [X]   No [ ]


Indicate the number of shares outstanding of each of the issuer's classes of
common stock, as of the latest practicable date.


Common stock, par value $.10 per share                   1,578,309 shares
--------------------------------------          --------------------------------
             (class)                            Outstanding as of August 7, 2000




<PAGE>   2

                         FIRST NATIONAL BANCSHARES, INC.
                               Index to Form 10-Q
                       For the quarter Ended June 30, 2000

                                                                            Page
PART I.  FINANCIAL INFORMATION

         Item 1. Financial Statements

                 Condensed Consolidated Balance Sheets,
                 June 30, 2000 and December 31, 1999                         1

                 Condensed Consolidated Statements
                 of Income for the six months ended
                 June 30, 2000 and 1999                                      3

                 Condensed Consolidated Statements of
                 Cash Flows for the six months ended
                 June 30, 2000 and June 30, 1999                             4

         Item 2. Managements Discussion and Analysis of
                 Financial Condition and Results of Operations               6

         Item 3. Quantitative and Qualitative Disclosure About Market Risk  10

PART II. OTHER INFORMATION.

         Item 1. Legal Proceedings                                          12

         Item 2. Changes in Securities and Use of Proceeds                  12

         Item 3. Defaults under Senior Securities                           12

         Item 4. Submission of Matters to a vote of Security Holders        12

         Item 5. Other Information.                                         12

         Item 6. Exhibits and Reports on Form 8-K                           12

SIGNATURES                                                                  13

         Exhibit Index                                                      14




<PAGE>   3

PART I.  FINANCIAL INFORMATION

         Item 1. Financial Statements

                         FIRST NATIONAL BANCSHARES, INC.
                           Consolidated Balance Sheet

                                 Assets (000's)

                                                   June 30           December 31
                                                 -----------         -----------
                                                     2000                1999
                                                 -----------         -----------
                                                 (Unaudited)             **

Cash and Due from Banks                               4,524              6,578
Interest Bearing Bank Balances                          301                395
Federal Funds Sold                                        0                  0
Investment Securities,                               40,474             42,100
Unrecognized securities gains                        (1,625)            (1,251)
Loans                                               135,486            122,007
Less allowance for credit losses                     (1,355)            (1,254)
Deferred Loan Fees (earned)                             (34)               (46)
Premises and Equip, Net                               4,843              4,856
Accrued Interest Rec                                  1,118                964
Other Assets                                          1,274                586
Deferred Income Tax Charges                             968                838
Other R.E. and other assets owned                        47                 29
                                                  ---------          ---------
Total Assets                                      $ 186,020          $ 175,802
                                                  ---------          ---------

** Condensed from audited financial statements
















                                       1
<PAGE>   4

                      Liabilities and Stockholders' Equity

                                                     June 30         December 31
                                                    ---------        -----------
                                                       2000              1999
                                                    ---------        -----------
Liabilities
  Deposits
         Demand, non-interest bearing                  20,601           20,528
         Demand int. bearing                           19,025           19,088
         Time (CD's, MM's, &
                  Savings Accounts)                   121,661          112,568
                                                    ---------        ---------

                  TOTAL DEPOSITS                      161,287          152,184
                                                    ---------        ---------

Repurchase Agreements                                   4,351            3,532
Capital Lease Obligation                                  484              505
Accrued Interest Payable                                1,272            1,051
Accounts Payable and other Liabilities                    469              455
Fed Funds Purchased and other
  Short Term Borrowings                                 5,000            5,500
                                                    ---------        ---------

         TOTAL LIABILITIES                            172,862          163,227
                                                    ---------        ---------

Stockholders' Equity:
 Common stock, par value $.10 per share;
   Authorized 2,500,000 shares;
   Issued and outstanding 1,578,309 shares                158              158
 Capital Surplus                                       14,119            9,670
 Unrecognized securities gains                         (1,014)            (793)
 Retained Earnings                                       (105)           3,540
                                                    ---------        ---------

         Net stockholder's equity                      13,158           12,575
                                                    ---------        ---------

Total Liab. & stkhldr's equity                      $ 186,020        $ 175,802
                                                    ---------        ---------




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<PAGE>   5

FIRST NATIONAL BANCSHARES, INC

                               STATEMENT OF INCOME
                FOR THE PERIOD JANUARY 1 THROUGH JUNE 30 (000'S)

                                                   2000            1999
                                                  ------          ------
Interest Income:
 Loans (excluding fees)                            5,534           4,162
 Loan Fees                                            76              34
 Investment securities:
   Taxable                                           958           1,165
   Exempt from Federal Taxes                         181             135
 Interest Bearing Bank Balances                       99             177
 Federal funds sold                                    0              21
                                                  ------          ------
         Total Interest Income                     6,748           5,694

Interest expense                                   3,419           2,778
                                                  ------          ------
         NET INTEREST INCOME                       3,330           2,916

Provision for credit loss                            105              65
                                                  ------          ------
Net Interest Income
  After Provision for Credit Losses                3,225           2,850
                                                  ------
Other operating income:
  Service charges on deposit accounts                200             198
  Investment sec. gains                                0              34
  Trust Fees                                         260             206
  Other Income                                       338             250
                                                  ------          ------
         Total Other Operating Income                798             688
Other operating expenses:
 Salaries and employee benefits                    1,497           1,288
 Occupancy expense of bank premises                  281             255
 Equipment expense                                   208             207
 Other expenses                                      846             842
                                                  ------          ------

         Total Other operating expenses            2,832           2,592
                                                  ------          ------

         Profit Before Tax                         1,190             947

Estimated State and Federal Income Taxes             389             318
                                                  ------          ------

         PROFIT AFTER TAX                         $  801          $  629
                                                  ------          ------




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<PAGE>   6

                            STATEMENTS OF CASH FLOWS
                                     (000'S)
                For the Period January 1 through June 30 (000's)

<TABLE>
<CAPTION>

                                                                           2000               1999
                                                                         --------           -------
<S>                                                                      <C>                <C>
OPERATING ACTIVITIES
Net Income                                                                    801               629
 Adjustments to reconcile net income to
 cash provided by operating activities:
  Depreciation & leasehold amortization                                       201               200
  Allowance for loan losses (net of charge offs)                              101                20
  Deferred income taxes                                                      (128)             (383)
  Decrease in accrued interest receivable                                    (154)              (29)
  Increase (decrease) in accrued interest payable                             221              (152)
  Increase (decrease) in accounts payable and other liabilities                99               256
  Decrease (increase) in other assets                                        (652)             (132)
                                                                         --------           -------
Net cash provided by operating activities                                     489               417

INVESTING ACTIVITIES
 Proceeds from sales and maturities of investment
   securities net of purchases                                              1,647            (7,645)
 Loans originated, net of principal collections                           (13,467)           (6,182)
 Capital expenditures                                                        (206)              (46)
 Proceeds from sale of other R. E. and assets owned                             0                47
 Increase (decrease) in federal funds purchased                              (500)            2,750
 Decrease (increase) in federal funds sold                                      0             6,603
                                                                         --------           -------
 Net cash provided (used) by investing activities                         (12,526)           (4,473)

FINANCING ACTIVITIES
Net increase (decrease) in demand deposits                                     10              (471)
Net increase (decrease) time deposits                                       9,093             2,486
Increase (decrease) in securities sold under
  agreements to repurchase                                                    819               965
Dividends paid                                                                  0                 0
Proceeds from issuance of common stock                                          6                 0
Retirement of common stock                                                      0                 0
Principal payments under capital lease obligation                             (21)              (19)
                                                                         --------           -------
Net cash (used) provided by financing activities                            9,907             2,931
                                                                         --------           -------

Net increase in cash and due from banks                                    (2,130)           (1,125)

Cash and due from banks at beginning of year                                6,944             4,526
                                                                         --------           -------
Cash and due from banks at end of quarter                                $  4,814           $ 3,391
                                                                         --------           -------

SCHEDULE OF NON-CASH INVESTING ACTIVITIES
Loans transferred to other real estate owned                             $      0           $    44
                                                                         --------           -------
</TABLE>




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<PAGE>   7

                     NOTES TO CONDENSED FINANCIAL STATEMENTS

NOTE 1 - BASIS OF FINANCIAL REPORTING

The accompanying unaudited condensed financial statements have been prepared in
accordance with instructions to Form 10-Q and do not include all of the
information and footnotes required by generally accepted accounting principles
for complete financial statements. In the opinion of management, all normal and
recurring adjustments necessary for fair presentation of such financial
statements have been included. For further information, refer to the
consolidated financial statements and the notes thereto included in the Bank's
annual report on Form 10-K for the year ended December 31, 1999.

Results for the six month period ended June 30, 2000, may not necessarily be
indicative of those to be expected for the entire year.















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<PAGE>   8


ITEM 2.  MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS
         OF OPERATIONS.

Overview.

         The First National Bank of Manatee (the Bank) commenced operations on
July 18, 1986. The Bank's activities since inception have consisted of
accepting deposits, originating a variety of loans. The Bank's first branch was
opened on Anna Maria Island (5 miles west of the main office) in October, 1994.
The second branch was opened in May of 1996 on State Road 64 (5 miles east of
the main office). In January of 1997 year, the bank opened its third branch on
State Road 70 (8 miles southeast of the main office). In December of 1997, the
bank acquired a site at University Blvd. and Lakewood Ranch Blvd. for a future
branch. The bank also opened a Trust Department in March of 1995. The Bank, as
a local independent bank, follows a philosophy of developing its equity and
deposit base and focusing its lending activities within its community. The
Bank's underlying lending policy has been and is anticipated to continue being
directed toward better-than-normal credit risks.

         On January 1, 1999 the Bank was merged into First National Bancshares,
Inc., a Florida corporation (the Holding Company). The Holding Company was
formed specifically for the purpose of having the Bank merged into it. At the
time of the merger, the Holding Company had assets of $128,000 and a net worth
of ($55,000). The Holding Company is now a one bank holding company with no
other subsidiaries than the Bank. Therefore, there are no significant
adjustments from the financial information of the Bank to the consolidated
financial information for the Holding Company.

         The following discussion and analysis is based on the Holding
Company's financial condition and results of operations for the period from
January 1, 2000 through June 30, 2000. This discussion and analysis should be
read in conjunction with the financial statement summaries of the Holding
Company, included elsewhere in this quarterly report.

Results of Operations.

         Earnings in the first two quarters of 2000 were up $172,000 or 27%
compared to earnings in the same period last year This was a direct result of
net interest income increasing by $414,000. This increased net interest income
was offset by a $238,000 increase in overhead which was softened by a $110,000
increase in other operating revenues. The Bank's contribution of $105,000 to
loan loss reserve was $40,000 higher than last year and was the result of
increased loan volume. The increase in operating expenses from last year was
due mostly to increased salary expenses as a result of increased staffing to
support growth.

Net Interest Income. The major component of the Bank's earning capacity is net
interest income, which represents the difference or spread between interest
income on earning assets and interest bearing liabilities, primarily deposits.
The spread is considered positive when rate-sensitive




                                       6
<PAGE>   9

assets exceed rate-sensitive liabilities, and negative when rate-sensitive
liabilities exceed rate sensitive assets. Net interest income is also affected
by changes in interest rates earned and paid, and by changes in the volume of
interest-earning assets and interest-bearing liabilities. To the extent
possible, the Bank follows a strategy intended to insulate the Bank's interest
rate spread from adverse changes in interest rates by maintaining spreads
through the adjustability of its earning assets and interest-bearing
liabilities. On June 30, 2000, the Bank's loan portfolio had a reasonable ratio
of repriceability within one year.

         The Bank had good growth in its loan portfolio outstandings when
compared to last year and this has significantly increased net interest income.
Net interest income for six months in 2000 was $3,330,000 compared to
$2,916,000 in 1999.

Interest Earning Assets. Real estate related loans at June 30, 2000, accounted
for a majority of the bank's loan portfolio. Most of the mortgages are variable
rate loans and are adjustable each one to five years. Thus, volatile interest
rates can result in the real estate loans lagging market conditions. In early
1999, rates were stabile allowing the portfolio to keep pace with market rates.
In the second quarter of 1999, rates began to rise modestly and accelerated
later in the year. This has caused temporary fluctuations in the bank's net
interest income until its balance sheet reprices to the new market rates.

         The Bank's investment portfolio is concentrated primarily in U.S.
Government agencies and corporations. About 22% of the Bank's investment
portfolio re-prices in one year. Due to rising interest rates, the Bank's
Available-for-Sale portfolio has a market value of about $1,251,000 below book
value.

Non-interest Earning Assets. Non-interest earning assets accounted for 6.9% of
total assets on June 30, 2000, and primarily consisted of cash and due from
banks, capitalized lease, equipment and branches, deferred taxes, and accrued
interest receivable.

Funding Sources. The primary source of funds for the Bank's lending and
investment activities is deposits. At June 30, 2000 the Bank's total deposits
were $161.3 million plus $4.4 million in repurchase agreements. The Bank's
deposits are highly concentrated in interest-bearing accounts, which is typical
for the Bank's market area. The Bank has 12% of its deposits in NOW Accounts
and 75% of its deposits in Savings, MMA's and CD deposits. Despite the high
concentration of certificates of deposit, the Bank does not anticipate the
maturity of such certificates to affect the Bank's liquidity, as management
believes that the high concentration was primarily due to customer
relationships and not higher than market rates. The Bank is not in the practice
of paying above market rates on deposits.

Non-interest Income. The Bank's non-interest income for the six month period
ended June 30, 2000 was $798,000 including $260,000 from its Trust Department.
Periodic security transactions generate investment gains or losses and are
primarily a result of tax management considerations and liquidity requirements.
The bank has had no security gains in 2000. The other significant items of
non-interest income represented service charges on deposit accounts,
annuity/mutual fund sales, and merchant credit card account income.




                                       7
<PAGE>   10


Non-interest Expense. The Bank's non-interest expense for the six month period
ended June 30, 2000 was $2,832,000 including $1,497,000 of salaries and
employee benefits. The Bank's occupancy and equipment expenses for the period
ended June 30, 2000 were $281,000. Non-interest expense was up from $2,592,000
in 1999. The increase in expense is primarily due to the Bank's increased staff
to support the bank's growth and the bank's expanded efforts in departments
generating other operating income.

Allowance for Credit Losses. The allowance for credit losses is established
through a provision for credit losses charged to expenses. Loans are charged
against the allowance for credit losses when management believes that the
collectability of the principal is unlikely. The allowance is an amount that
management believes will be adequate to absorb losses inherent in existing
loans and commitments to extend credit based on evaluations of the
collectability and prior loan loss experience of loans and commitments to
extend credit. The evaluations take into consideration such factors as changes
in the nature and volume of the loan portfolio, overall portfolio quality,
review of specific problem loans, and current economic conditions that may
affect the borrowers' ability to pay.

         An allowance for loan loss expense of $105,000 was charged to
operating expenses for the six month period ended June 30, 2000. The Bank had
net charge offs during this period of $4,000. The Bank has a total of
$1,355,000 reserved for future loan losses.

         Loans on which the accrual of interest has been discontinued are
designated as non-accrual loans. Accrual of interest on loans is discontinued
either when reasonable doubt exists as to the full, timely collection of
interest or when a loan becomes contractually past due by 90 days or more with
respect to interest or principal. When a loan is placed on non-accrual status,
all interest previously accrued but not collected is reversed against current
period interest income unless it is adequately secured. Income on such loans is
then recognized only to the extent that cash is received and the future
collection of principal is probable. Interest accruals are resumed on such
loans only when they are brought fully current with respect to interest and
principal and when in the judgment of management, the loans are estimated to be
fully collectible as to both principal and interest. The bank had one
non-accrual real estate loan at June 30, 2000 totaling $1,102,000. Where
appropriate, the Bank makes specific reserves for future losses on
non-performing loans. The Bank has set up no specific reserve on this loan
because it estimates that the collateral is adequate to satisfy the debt.

         The bank also has no other real estate owned at June 30,1999.

Capital Resources. In the normal course of business, the capital position of
the Bank is reviewed by management and regulatory authorities. The Comptroller
of the Currency has specified guidelines for purposes of evaluating a bank's
capital adequacy. Currently, banks must maintain a minimum primary capital
ratio of capital-to-assets of 4%. Primary capital includes the Bank's
stockholders' equity, subordinated debt, and the allowance for credit losses.
At June 30, 2000, the




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<PAGE>   11

Bank's primary capital ratio was approximately 7.6%. In 1991, the Comptroller
began evaluating banks' capital on a risk basis i.e. more capital will be
required for commercial loans than for residential real estate loan and even
less will be required for government bonds. The Comptroller will require a
minimum of an 8% capital ratio under this risk based method. Currently the Bank
has a risk based capital ratio in excess of 11.2%, or more than double the
required amount.

Liquidity. Management of the Bank continually evaluates its liquidity position.
Management believes that the Bank's investment portfolio, when combined with
interest bearing bank balances and Fed Funds sold, provides adequate liquidity
to meet the Bank's needs. As noted in "Funding Sources" above, management
believes that the high concentration of time deposits is primarily due to
customer relationships and not to higher-than-market rates and, thus, do not
present any unusual liquidity risk. In addition, the bank has established
borrowing lines with correspondent banks, and with the Federal Home Loan Bank
to cover liquidity needs.

Impact of Inflation and Changing Prices. Unlike most industrial companies,
virtually all of the Bank's assets and liabilities are monetary in nature. As a
result, interest rates have a more significant impact on the Bank's performance
than do the effects of inflation. Interest rates do not necessarily move in the
same direction or with the same magnitude as the prices of goods and services,
since such prices are affected by inflation. In the current interest rate
environment, liquidity and the maturity structure of a financial institution's
assets and liabilities are also critical to the maintenance of acceptable
performance levels.




                                       9
<PAGE>   12

ITEM 3.  QUANTITATIVE AND QUALITATIVE DISCLOSURE ABOUT MARKET RISK

         The Bank periodically performs asset/liability analysis to assess the
Bank's sensitivity to changing market conditions.

         The primary functions of asset/liability management is to assure
adequate liquidity and maintain an appropriate balance between
interest-sensitive earning assets and interest-bearing liabilities. Liquidity
management involves the ability to meet the cash flow requirements of customers
who may be either depositors wanting to withdraw funds or borrowers needing
assurance that sufficient funds will be available to meet their credit needs.
Interest rate sensitivity management seeks to avoid fluctuating net interest
margins and to enhance consistent growth of net interest income through periods
of changing interest rates.

         Marketable investment securities, particularly those of shorter
maturities, are a principal source of asset liquidity. Securities maturing or
expected to be called within one year or less amounted to $3,952,000 at June
30, 2000 representing 10% of the investment securities portfolio, a decrease
from $8,350,000 last year. This is due to rising rates over the last year
resulting in slower repayment on some bonds.

         Federal funds and lines of credit with other banks also provide the
bank with sources of funds for meeting its liquidity needs. At year-end, the
bank had lines of credit established with other banking institutions totaling
$23,500,000.

         Brokered deposits are deposit instruments, such as certificates of
deposit, bank investment contracts and certain municipal investment contracts
that are issued through brokers who then offer and/or sell these deposit
instruments to one or more investors. The Bank does not currently purchase or
sell brokered deposits.

         Maturities of time certificates of deposit and other time deposits of
$100,000 or more, outstanding at June 30, 2000, are summarized as follows:

                                                    Time Deposits
                                                    -------------
                                               (thousands of dollars)

         3 months or less                             $ 5,206
         Over 3 through 12 months                      12,962
         Over 12 months                                 6,561
                                                      -------
         Total                                        $24,729

         Interest rate sensitivity varies with different types of interest
earning assets and interest-bearing liabilities. Overnight federal funds on
which rates change daily and loans which are tied to the prime rate differ
considerably from long-term investment securities and fixed-rate loans.
Similarly, time deposits over $100,000 and money market accounts are much more
interest rate sensitive than savings accounts. The shorter term interest rate
sensitivities are key to measuring the interest sensitivity gap, or excess
interest-sensitive earning assets over interest-bearing liabilities.




                                      10
<PAGE>   13

         The following table shows the interest sensitivity gaps for four
different time intervals as of March 31, 2000. For the first year,
interest-sensitive assets exceed liabilities by $24,806,000. For the next two
years, liabilities reprice more rapidly than assets lowering the bank's asset
sensitive position to an essentially balanced position for the three year
period. The excess of interest-bearing liabilities over interest-earning assets
for the one-to-three year period is primarily related to the longer maturities
of CD's and NOW and MMA accounts that are regarded as much less rate sensitive.

                                                 As of December 31
                                               (thousands of dollars)
                                       0-90      91-365       1-3       Over 3
                                       Days       Days       Years       Years
                                     -------    -------    --------    -------

Interest-sensitive assets            $57,103    $53,692    $ 31,069    $30,674
Interest-sensitive liabilities        44,475     41,514      55,957      3,888
                                     -------    -------    --------    -------
Interest sensitivity gap              12,628     12,178     (24,888)    26,786
Cumulative gap                       $12,628    $24,806     $   (82)    26,704

         The primary interest sensitive assets and liabilities in the one-year
maturity range are loans and time deposits. Trying to minimize this gap while
maintaining earnings is a continual challenge in a changing interest rate
environment and one of the objectives of the Bank's asset/liability management
strategy.




                                      11
<PAGE>   14

Part II. Other Information

Item 1:  Legal Proceedings Against the Bank - None.

Item 2:  Changes in Securities and Use of Proceeds - None

Item 3:  Defaults under Senior Securities - None

Item 4:  Submission of Matters to a vote of Security Holders - None.

Item 5:  Other Information - None

Item 6:  Exhibits and Reports on Form 8-K


         Exhibits

                  a)       Plan of acquisition, reorganization, arrangement,
                           liquidation, or succession.

                           None

                  b)       Articles of incorporation and by-laws.

                           1)  A copy of the Amended and Restated Articles of
                               Incorporation of the Registrant is included as
                               Exhibit 3.A to the Registration Statement.

                           2)  A copy of the Bylaws of the Registrant is
                               included as Exhibit 3.B to this Registration
                               Statement.

                  c)       Instruments defining the rights of securities
                           holders, including indentures.

                           None

                  d)       Published report regarding matters submitted to vote
                           of security holders.

                           None

Reports on Form 8-K - None




                                      12
<PAGE>   15

                                       FIRST NATIONAL BANCSHARES, INC.


Date: August 9, 2000                   /s/ Glen W. Fausset
                                       ----------------------------------------
                                           Glen W. Fausset
                                           President and Director

















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<PAGE>   16
                                 EXHIBIT INDEX

Exhibit
  No.         Description
-------       -----------

 27.1         Financial Data Schedule (for SEC use only)























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