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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4/A</documentType>

    <periodOfReport>2016-12-14</periodOfReport>

    <dateOfOriginalSubmission>2016-12-14</dateOfOriginalSubmission>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001017793</issuerCik>
        <issuerName>SUN BANCORP INC /NJ/</issuerName>
        <issuerTradingSymbol>SNBC</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001228873</rptOwnerCik>
            <rptOwnerName>BROWN JEFFREY S</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O SUN BANCORP, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>350 FELLOWSHIP ROAD, SUITE 101</rptOwnerStreet2>
            <rptOwnerCity>MOUNT LAUREL</rptOwnerCity>
            <rptOwnerState>NJ</rptOwnerState>
            <rptOwnerZipCode>08054</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Commn Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>73279</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>NFI Road Rail, LLC</value>
                    <footnoteId id="F1"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">This amendment is being filed to correct the name of the entity with ownership of the securities.  The shares previously held by NFI Interactive Logistics Inc. have been transferred to NFI Road Rail, LLC as of December 2012.  The amount of securities beneficially owned and reported in Column 5 represents the total number of shares indirectly owned by the Reporting Person as amended by Form 4/A filed the date hereof amending a Form 4 filed on 8/11/2011.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Jeffrey S. Brown</signatureName>
        <signatureDate>2017-03-24</signatureDate>
    </ownerSignature>
</ownershipDocument>
