We have a small basement floor drain from which air blows when a toilet is flushed upstairs is this a problem?

My wife noticed that air blows out of a small floor drain in our basement when a toilet is flushed in our upstairs bathroom. Obviously the air is being forced out of the sewer line when the water from upstairs rushes down through the drain pipe. I think this is occurring because we have a dried out drain trap, however I don't want to fill a trap only to have the air blow out the water out with the next flush. My question is am I right about the drain trap or is there something else going on that I don't understand?