display alert by by using serverside code(works fine)

<asp:Button ID="ApproveButton" runat="server" CausesValidation="False" Text="ravi"
   
        OnClientClick="return confirm('Are you certain you want to approve this record?');"
        onclick="ApproveButton_Click" />

If the user clicks OK your normal click code will run but if they cancel the function returns false so the click won't be processed.