The one-alarm fire was set at about 4:45 p.m. in a trash can in a first-floor bathroom at 2415 University Ave., which houses the City Council chambers, administrative offices, and library, fire Chief Harold Schapelhouman said.
The fire was quickly controlled but required about 50 people to be evacuated, including students and staff at the library.
The three-story building's sprinkler system was not activated because the trash can was set back in a wall, which prevented the flames from spreading, Schapelhouman said.
No injuries were reported.
Tonight's City Council meeting was scheduled to begin at 7:30 p.m. but was canceled.
Police are following up on two juvenile suspects who were captured on surveillance video, Schapelhouman said.
He said the building would likely be open on Wednesday after it's aired out later tonight.