The police received calls from members of the public just before 6 pm yesterday evening reporting that the 17-year-old was carrying a handgun around Le Squez in St Clement.
Firearms officers arrived on the scene shortly after, and the teenager was arrested in Georgetown just after 7.30 pm.
The police also recovered an imitation firearm.
The boy has since been released on bail but anyone with information is asked to contact the police on 612612 or Crimestoppers anonymously on 0800 555111.