A 14-year-old boy was arrested at a Bronx school on Thursday after police discovered a loaded gun in the back of his moped — which was stolen, police and sources said.

The firearm was found around 10 a.m. outside of the J. M. Rapport School Career Development on Jackson Avenue in Mott Haven, according to police.

School safety agents on Wednesday saw the student on the moped acting suspiciously, and believed he may have been concealing a weapon, sources said.

On Thursday, the student again took the moped to school and parked it behind the building.

The agents, concerned about his behavior the previous day, investigated and found the loaded handgun stashed inside of the moped.

The student, whose name is not being released due to his age, was arrested.

The moped, which police learned was stolen, was also seized, sources said.

The teen was charged with criminal possession of a weapon on school grounds, criminal possession of a firearm and criminal possession of stolen property, police said.