Help!!! FBI will inteview me

I got a phone call from local FBI agent, he wants to interview me and asks some basic questions, he also mentions that this is not a big deal, just because I changed my visa status from f1 to h1 (a years ago).

Has anyone faced or known any case like this one?

I believe that I did nothing wrong and nothing that could be interesting from FBI's perspective. And I don't
think I have a skill that might interest them. I have graduated from a school here and am working for a computer company.

I would really appreciate if anyone can share information, experience and give me suggestions!

Thanks a lot!