validating passwords problem

Friends, I am working on password validation screen where I have two textboxes.(Password and retype password). I am validating both these textboxes using javascript under Login button.

And the serverside code behind event is redirecting to another aspx page. My problem is if i enter  different passwords in these textboxes it is automatically getting redirected to new page. The correct functionality is if the password entered in both TB is correct it should redirect to another page orelse it should not get redirected. But why it is happening?
...