The center, located in Hillsboro, Ore., said the monkeys escaped Friday when a worker closed the door to the male monkeys' home but forgot to fasten the lock, The (Portland) Oregonian reported Tuesday.
"The one (worker) who made the mistake has been here many, many years and is a very good employee," said Jim Newman, a spokesman for Oregon Health & Science University, which operates the primate center.
The center's head veterinarian, C.J. Doane, said the monkeys were tracked and recaptured during the weekend.
"I think they had a good time," Doane said. "I think they were enjoying the sunshine."
Newman said workers at the center are receiving extra training to help them prevent future monkey escapes.