use updateprogress of tool kit :hope this will help you
<asp:updatepanel id="ResultsUpdatePanel" runat="server">
<contenttemplate>
<div style="text-align:center;">
<asp:updateprogress id="UpdateProgress1" runat="server" associatedupdatepanelid="ResultsUpdatePanel" dynamiclayout="true">
<progresstemplate>
<img src="https://stackoverflow.com/questions/2813590/support/images/loading.gif">
</progresstemplate>
</asp:updateprogress>
</div>
//your control code
</contenttemplate>
</asp:updatepanel>