The tickets went on sale to season-ticket holders only on Tuesday morning and 57,342 were sold on the first day.
Nebraska announced the game was sold out 90 minutes after tickets went on sale to the general public on Wednesday morning.
Tickets cost $10 for adults and were free for Nebraska students and children.
Capacity for Memorial Stadium in Lincoln, Neb., is listed at 85,458.
"I want recruits to see that fan base and see how excited people are, and see that environment," Frost said Wednesday in an interview on ESPN2.
The Huskers have sold out 361 consecutive regular-season home games, an NCAA record. The April 21 scrimmage will mark the first spring sellout in Nebraska history.
Nebraska has drawn crowds of more than 60,000 for nine consecutive spring games and drew 78,312 last year to rank second nationally behind Ohio State's 80,149.
The Buckeyes announced a sellout on the day before that game as portions of Ohio Stadium were closed because of construction. Spring attendance at Ohio State topped 100,000 in 2016 to set a national record.
The existing Nebraska record for a spring game is 80,149, set in 2008, the first spring for former coach Bo Pelini.
Frost, a Nebraska native who was the starting quarterback of the Huskers' unbeaten 1997 team, directed Central Florida to a 13-0 finish in 2017, while Nebraska finished 5-7 in Mike Riley's third and final season.