going to form action page on alert box confirmation

i kept one form it contains one text box and one button, and i put the code like this <form action='/cgi-bin/sample.py?firstname=something' method='get' onsubmit='return validate(this);'> and i put validation for text box also

and when i press submit button without provideing any value alert box pop up, but when i press ok in the alert box it is navigating to the sample.py

i dont know what is the problem, i want it to be on the same page after alart box submission, is there any way???

help me out.....