You 100% should ask questions. What balog pal is saying is not a good idea. The interviewers are not going to try and decide if you are just so smart that you know everything about their company. You NEED to ask questions. It is your turn to interview them. They will be more impressed if you have detailed and specific questions to ask about their company.
Some good questions would be:
What is the work environment like at work?
Why have you stayed here, what keeps you coming back to work here?
Maybe something wasn't clear in the job description so ask about it, What would I be doing in this area? What is a normal day like at work?
DO RESEARCH ON THE COMPANY You guys seemed really involved in _ _ _ _ _ How can I get involved in that? Are you involved in that?
Remember people love to talk about themselves, so ask about them, related to work and geared toward some things that would help you choose the job if you got it.
EDIT: Also a good rule of thumb I go by is to have about 5-7 good questions thought up in my head and ask 3-4 of them. You want to have a few more thought up because it is likely that they are going to answer them already. You also want to stay engaged while asking questions. When they give an answer to your question ask a question that branches off their answer. If you ask a few good questions you will leave the interview just fine. Remember EYE CONTACT AND FIRM HANDSHAKE you want to start off on a good note and end on one as well.