Ajax does not work when submitting a form

[auriaks]

I have ajax script which uses function.php file [it is a registration form] to open. It opens it correctly, but when I submit the form I am redirected to function.php page... Why ajax wont let me submit it while It is loaded in my index.php page?

[I can post a code if it is needed]

All suggestions are welcome and thanks for your time..