Credit: Steve Granitz/

Girls just wanna have fun, and Sandra Bullock is no exception!

"I'm having such a good time tonight," the 47-year-old actress told ABC's Robin Roberts on the red carpet at Sunday's 84th Annual Academy Awards in L.A. "It's called sexy time. We're having sexy time tonight. Everything we're doing is going to be sexy."

Bullock, who won an Oscar in 2010, showed off her sexy backside in a head-turning Marchesa gown. "You find one [dress] and then you make your way through others, and you usually make your way back to your original choice," the actress -- who keeps her figure fit thanks to Body By Simone's Simone De La Rue -- said. "That's what happened."

After adopting son Louis, now 2, and going through a divorce from bad boy Jesse James, Bullock took a break from acting. She made her return to film in the 9/11 drama Extremely Loud & Incredibly Close, which is nominated for Best Picture.

"The book was extraordinary," Bullock said. "And to see it through a child's point of view is so completely than an adult's point of view because they know so little and they want to know so much that we can't possibly answer. I liked the challenge of it. I thought it was beautiful."