Police spokeswoman Jennifer Ciaccia said the school board told police there has not been confirmation that the man had the gun inside the school at this time.
He is reportedly an 11th grade student at the school, according to police.
Investigators said officers responded to the school around 2 p.m. Wednesday, Feb. 28.
The man was taken into custody without incident at 107th Street and St. Clair Avenue and a loaded .9mm handgun was recovered.
Police say they do not know if he threatened anyone with the gun.
Police found out about the incident after a student told a parent, the parent called authorities.
This story is developing, we will update this story as more information becomes available.