The 19-year-old had a .22 caliber handgun with him as he rode a bus from a local high school to a nearby vocational-education center, Anchorage School District officials said.
"As the student was getting off of the bus, the driver noticed the student had a weapon," said Heidi Embley, the district's spokeswoman, adding that police were called and the student was turned over to their custody.
The incident comes a day after Florida police arrested a 17-year-old boy who they said had material to make pipe bombs at his home and planned to cause mass casualties at his Tampa high school.
In that case, Tampa Police Chief Jane Castor told reporters that Jared Cano had hoped to "cause more casualties than were suffered at Columbine."
In the Alaska incident, no injuries or threats were reported, the school district said.
The Anchorage student, identified as Bryan Briggs, was in jail on Thursday facing a charge of misconduct involving a weapon, Anchorage Police Department spokeswoman Marlene Lammers said.
The school district said in a statement it would be seeking to expel Briggs under a zero-tolerance policy concerning weapons.
(Reporting by Yereth Rosen, editing by Dan Whitcomb and Cynthia Johnston)