An air mattress can be placed on a futon frame as long as the frame is able to support the weight of the mattress and the person sleeping on it. The average queen-sized air mattress weighs around 30 pounds, so make sure your futon frame can accommodate that much weight. You'll also want to make sure there's enough clearance between the bottom of the mattress and the top of the futon frame so that you can inflate or deflate the mattress without any issues. If everything looks good, go ahead and give it a try!