One room is very dusty and has dust build up on the air vent.

I have one room in the house that is very dusty. The walls get dust build up over a few months and the air vent itself looks like my air filters do after about one month. What would cause such a localized issue? Would a badly sealed duct system to that room cause this? If so, what is the best way to find the problem area?

Thanks,
Mike Gilbert