There will be a difference in weight, though it's most likely negligible.
Take for instance a cup. If you weigh it, it'll have the same weight as if you weigh it with a lid on top to trap the air.
However, let's say I was to take that cup, and really make it a cylinder, and fill it to 500 PSI... there's more mass of air in the system.
Because the ball is inflated, there will be a (
slight) difference in weight.
10,000 points to the first person that can calculate the weight difference between an inflated and uninflated ball... (30" diameter, 30 PSI, assume 1/8" wall thickness)
Matt