Hakop Jack Kaplanyan, 18, was arrested April 2, KTLA-TV, Los Angeles, reported. He was released on $200,000 bail and has been suspended from the university.
A hearing is scheduled April 25.
Police said the alleged victim, who described Kaplanyan as an acquaintance, reported April 2 he had sexually assaulted her that day in a UCLA residence hall.
Kaplanyan's mother, Marine, told KTLA Monday her son is innocent.
"It's so easy for them to just accuse a person without like telling the truth," she said during an interview at her home in Glendale. "My son is innocent, I can tell you that and we're going to prove that, because he's not one of those guys."
Kaplanyan played water polo for Hoover High School where he was a three-time first team selection for the California Interscholastic Federation and was named most valuable player twice. He set a CIF record for goals scored in his sophomore year.