Castillo's show is scheduled to be simulcast on MTV.com Thursday from Radio City Music Hall where the ceremonies are being held, the New York Daily News reported.
The awards show, hosted by Jack Black, returned to New York after being held several years in Miami.
"It's going to be everything that happens behind the scenes," Castillo said. "It's totally live! You really never know what's going to happen."
Castillo, 26, was Miss USA in 2003. She's also appeared on sitcoms, including "Half & Half" and "My Wife and Kids."
The bilingual MTV host, who was born in Massachusetts but is of Puerto Rican and Dominican descent, is MTV's first Latina veejay since Daisy Fuentes in the mid-1990s.
"This is my job now," Castillo said, "and, hopefully, maybe in a few years, I'll be back as an actor, and I'll be the one being interviewed!"