Do I have to disclose I am in a fulltime graduate program when being asked on a job application? Options are yes, no or non-applicable. I prefer not to disclose that I am, but fear I risk falsifying information if I indicate that I am not. Is it okay to write non-applicable? Thank you.

If it does not effect the job, then it is NA

I have to disagree with Fr_Chuck on this. If the application asks a specific question, then you should answer as truthfully as you can. You don't tell us what the nature of the job or your graduate studies are, so it's impossible to tell whether it's applicable to the application. In addition, I would expect your resume mentions your graduate studies, including your anticipated graduation date, right? So what's the point of trying to hide it?