It could be. Try switching the pump and filter to the other side and see if they follow. Or try moving the skimmer and see if they stay away from it.
Are your chemical levels normal? Temperature? If they're hanging out by the air source, is the water too warm? What kind of filter do you have? Maybe they're hanging out by the filter because of something in the water they don't like. What are the pH and ammonia levels? Do you add anything to water?
What kind of fish? Are they fish that like current, or fish that prefer calm water?
On second thought, I don't know anything about saltwater tanks or fish. It might be worth moving some of the equipment around to see if that's WHAT the problem is, but I have no advice on how to fix it. Sorry!