Patrick Henry High School in north Minneapolis has been placed on lockdown.
It comes after a man with a gun was seen stepping off a city bus nearby.
The school was placed on lockdown after a call came in from the school at about 3:43 p.m., it's now being evacuated while the school is searched.
Minneapolis police spokesperson Sgt. Darcy Horn told GoMN that the preliminary information they have is that a male with a gun got off the bus and then ran.
"Right now we are searching the school and the school is being evacuated for precaution."
Minneapolis police said it's not sure at this stage if the person ran into the school or not, but Minneapolis Public Schools said that was the case.
It also tweeted that the incident happened after most students had left for the day.
Schools across Minnesota have been on alert after the Florida school shooting almost two weeks ago that left 17 dead.
It has prompted a wave of copycat threats against schools, with those in Orono, Hill City and Woodbury among the Minnesota schools receiving them.