About 20 revellers drinking outside Degree bar dived for cover after the promotions worker threatened them with a black imitation pistol about 8pm on Friday.
Witnesses said they heard someone shout "he's got a gun" and outdoor drinkers dived behind their tables.
Degree manager Steph Kurtovich said: "This guy with bandages on his hands pointed a gun at customers sitting outside. They were pretty terrified."
The stunt, to promote the release of Xbox title Splinter Cell Evolution, was condemned by police.
Senior Sergeant Ben Offner said officers could not tell the gun was made of plastic until they had taken it from the actor.
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