Web Forms :: 1.1 - Button Post Back After Javascript Execution

I have created a listbox that the selected items would remove by using javascript once I clicked on a server button. Below is the code I'm using

<asp:button id="btnSelected" Runat="server" CssClass="InputFormObject" Text=">" ></asp:button>
<script language="javascript">
function removeOptions(selectbox)
{
var i;
for(i=selectbox.options.length-1;i>=0;i--)
{
if(selectbox.options[i].selected)
selectbox.remove(i);
}
return false;
}
</script>

private void Page_Load(object sender, System.EventArgs e).......................