How to prevent an asp:CheckBox control in an asp:GridView from causing postback when checked

I have an asp:CheckBox in an asp:GridView that causes postback when checked. I'd like to prevent postback. I'd also like to know why the same control doesn't cause postback when it's in an asp:Panel(ModalPopExtender)

<asp:GridView ID="GridViewGroups" runat="server" class="table table-striped table-bordered sourced-data dataTable "OnRowDataBound="GridViewGroups_RowDataBound" >
   <Columns>
     <asp:TemplateField>
      <ItemTemplate>
        <asp:CheckBox ID="chkRow2" class="icheckbox_polaris" runat="server" AutoPostBack="false" />
          </ItemTemplate>
       </asp:TemplateField>
     </Columns>                                                                                
</asp:GridView>