<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

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    <periodOfReport>2018-05-21</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
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        <issuerName>FNB BANCORP/CA/</issuerName>
        <issuerTradingSymbol>fnbg</issuerTradingSymbol>
    </issuer>

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        <reportingOwnerId>
            <rptOwnerCik>0001223822</rptOwnerCik>
            <rptOwnerName>ATWOOD THOMAS G</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1></rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity></rptOwnerCity>
            <rptOwnerState></rptOwnerState>
            <rptOwnerZipCode></rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
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            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

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                <transactionPricePerShare>
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                </sharesOwnedFollowingTransaction>
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            <ownershipNature>
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                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

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                <transactionAcquiredDisposedCode>
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            <expirationDate>
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                <transactionPricePerShare>
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            <exerciseDate>
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            <transactionDate>
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            <transactionCoding>
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            <transactionTimeliness>
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                <transactionPricePerShare>
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                <transactionAcquiredDisposedCode>
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                </transactionAcquiredDisposedCode>
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            <exerciseDate>
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            <expirationDate>
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            <underlyingSecurity>
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                </sharesOwnedFollowingTransaction>
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        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
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            <transactionTimeliness>
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            <transactionAmounts>
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                <transactionPricePerShare>
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            <exerciseDate>
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            <expirationDate>
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        </derivativeTransaction>
    </derivativeTable>

    <ownerSignature>
        <signatureName>THOMAS G. ATWOOD</signatureName>
        <signatureDate>2018-05-23</signatureDate>
    </ownerSignature>
</ownershipDocument>
