You have two option for that
1) Set AutoPostBack="False"
if you want AutoPostBack="True"
then,
2) Use UpdatePanel...
<asp:scriptmanager id=""ScriptManager1"" runat=""server"><br" mode="hold" xmlns:asp="#unknown" /> </asp:ScriptManager>
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
Put checkbox here...
</ContentTemplate>
</asp:UpdatePanel>