It happened around 11:15 Saturday morning on the 300 block of North Scott Street.
18-year-old Michael Colon's mother found the gun after looking in his backpack after the two had an argument.
Police say she was concerned that he was keeping late hours and hanging out in high crime areas.
Upon making the discovery she informed police.
Authorities say Colon is a convicted felon and prohibited from possessing firearms.
Colon was arraigned and later released after posting $10,000 secured bond.