No one reported shots being fired or injuries. It was not immediately clear whether the person in custody was tied to the original report and whether it was real or a hoax. Students were told to return to their normal routine about three hours later.
Campus police said they asked the Tampa police bomb team to investigate the belongings of the person in custody.
Lt. Meg Ross, of the USF Police Department, said a man was apprehended after he stood up on a campus bus and stated that he was the person authorities were looking for. Police responded to the scene and were able to get him off the bus.
"As I understand it, he did respond to our commands," Ross said.
A second person who was reportedly carrying a knife on campus was detained, but police said they believe it was unrelated.
The first call came in at 1:36 p.m. to the Hillsborough County Sheriff's Office, which transferred it to campus police.
A siren interrupted classes. An announcement over a loud speaker said there was an intruder and students should stay inside and lock their doors, said Amanda Barnes, an 18-year-old international studies major.
Administrators also sent several text messages to students.
"A lot of people were like, 'OK. I'm going to go up to my room, and no big deal,'" Barnes told The Associated Press. "A couple of people were like, 'Oh my God. I'm so scared.'"
Student Hannah Quill told the St. Petersburg Times what she saw and heard.
"It sounded like one of those tornado alarms up north," she said. "Everyone is like in classrooms on lockdown. I saw quite a few police cars heading towards the front of campus."
The name of the man who was on the bus was not released, and Ross could not say if he was a student.
"We cannot determine as of yet whether it is the person we were looking for," she said. "He's being questioned and we're trying to determine that at this point."
At about 3:30 p.m., police also reported a man wearing a black tank top and cowboy hat, carrying a black puppy and a large hunting knife on campus.
Ross said the man was being questioned, but it didn't seem related to the earlier report of a man carrying a gun and a bomb.
Associated Press writers Michael Schneider in Orlando and Tamara Lush in Miami contributed to this report.