Armed police with dogs arrested a 25-year-old man at the University of Lincoln earlier today.
Officers were been seen outside the Great Central Library near the Enterprise building on the University campus.
The man, who is thought not to be a student, was arrested on behalf of Nottinghamshire Police.
Lincolnshire Police apologised for "any alarm caused".
The university posted on Twitter: “We had some police presence on campus earlier today just outside the library.
“We did temporarily ask students to stay in the library whilst police handled an incident. We’re grateful for the patience and understanding of staff and students.”