Deputies said the child discovered the loaded semi-automatic pistol in a closet in the home on the 20100 block of Carlisle Road.
They said he picked up the gun and accidentally fired through the wall. The bullet struck a man who was on a couch in the next room. The victim was hit in the back of the neck, but he was expected to recover.
Jayquan Crittenden, 21, was arrested on suspicion of child endangerment and negligent storage of a firearm.