Ten minutes into the 11 a.m. class, he said, a campus police officer arrived and told the students that they had to evacuate because of a bomb threat. Mr. Fitzpatrick said he tried to go back to his dorm, but it, too, had been emptied because of a threat. Later that day, his 3 p.m. class was canceled, he said, again because of an evacuation.

“I have to admit, it made me a little bit uneasy to know that the place you sleep could be threatened,” he said.

The mood on campus has shifted in recent days, he said. “I think that we started off thinking it was a joke,” he said. “Then it got annoying. Now, at this point — I won’t lie — I got a little bit scared.”

While Mr. Fitzpatrick said he intended to remain on campus through final exams, which begin on April 23, he said other students had packed and headed home or moved off campus. “They just can’t deal with it,” he said.

Tyler McLaughlin, a senior studying math and molecular biology, said he had skipped classes because of the repeated bomb threats. Having to wait in a line to get into the Cathedral of Learning while the police check IDs has limited how often Mr. McLaughlin uses the building, the university’s most prominent.

Alexander Cull of Doylestown, Pa., a sophomore studying molecular biology, said that some exams were interrupted by evacuations, and that now he was taking all of those tests online. He said that the day before he had waited in line for half an hour to have his ID checked to get into a class.

Mr. Cull said he had offered some friends a space at his off-campus apartment. Other students have set up a Facebook page and a Google spreadsheet with information about off-campus accommodations for those dormitory residents weary of standing for hours outside their residence halls while bomb squads sweep for devices.