I have a vent in my ceiling into the attic. The attic has two small fans - I believe they serve the purspose of regulating the attic temp for the roof and they are not attic/house fans. My question is - do I need to have the vent from my ceiling into the attic or is it OK if I removed the vent and replaced it with a piece of solid wood?

You could probably cover the vent without doing any harm - probably - but it would be nice to know things like what room is it in and why was it put there in the first place? Can it be opened and closed? Does it vent directly into the attic or is it connected to a tube of some sort? (If so, where does that go?)
I don't think anyone can give you a good answer without more info.

Thanks for reply and I'll clarify. The vent is on the ceiling in the hallway. It's a square with vents that also acts as an entry point into the attic. I don't know exactly why it's there, but my assumption is that it was put there as an entry point into the attic. I just don't know why they used a vent instead of a piece of plywood. There is nothing attached to it - just piece of plastic with vents. The rest of the attic is empty with the exception of an AC unit with ducts and twan AC o attic fans with thermostats.