Error in regular expression validaator

I am using visual studio 2012 asp.net 4.5. i take a textbox on which I  am entering a password and set a regular expression validator that user must enter 3 letters and 2 digits. My problem is that it must show error message after pressing submit button. But it shows error msg when we press tab from that  textbox. i.e it's performing client side validation that I don't want. It must show error msg after pressing submit button. How I can do that? whether there is problem in my code?