The boy was among a dozen or so people " blocking the business entrance, playing loud music, and consuming alcoholic beverages" in the middle of the 100 block of North Main Street, Public Safety Director Jerry Speziale said.
Detectives Yamil Pimienta, John Traynor, Mohamed Bashir and Levis Qirjako approached to break up the group when they saw the boy trying to hide the gun and immediately took him into custody, Speziale said.
A 15-year-old boy who was with him ran and was found in a rear yard on Watson Street, the director said.
Juvenile Division detectives took custody of both boys. The gun was sent to the New Jersey State Police laboratory to determine whether it was used in any crimes.
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