Philip Storey, 41, of Council Bluffs, Iowa, was arrested on Friday on campus on suspicion of making terroristic threats.
UNL's assistant police chief, Carl Oestmann, and jail officials did not know whether he had an attorney.
A message left at a number listed for him in Council Bluffs wasn't immediately returned.
Oestmann, said Storey approached a student worker in the campus' landscape services department about 8 a.m. Thursday. Storey threatened "he would kill her" or would send someone to harm her if she continued to remove his signs, Oestmann said.
Campaign signs aren't allowed on university property.
Storey is an independent write-in candidate seeking the U.S. Senate seat held by Republican Chuck Grassley. The five-term incumbent and Democratic challenger Roxanne Conlin are on the ballots for Tuesday's election.