validation control in C#

hi
my code for comare validator is
<asp:CompareValidator ID="CompareValidator1" runat="server"                 ErrorMessage="Password mismatch"  ControlToValidate="txtpassword"                 ControlToCompare="txtconfirmpassword"></asp:CompareValidator>
but it is showing error msg when mouse over txtconfirmpassword
and txtconfirmpassword is blank
it should only dispalyed only when i entered