Actor Kelsey Grammer says he has "found great peace" in his Christian faith and won't apologise for it as his latest movie continues to defy expectations at the box office.

Grammer, best known for his role in hit TV comedy Frasier, has a starring role in new Christian movie, Jesus Revolution, about the conversion of American evangelist and megachurch pastor Greg Laurie.

The movie surprised critics by taking $15m at the box office in its opening weekend.

Grammer plays the role Pastor Chuck Smith, Laurie's mentor.

The synopsis for the Lionsgate movie says, "'In the 1970s, Greg Laurie and a sea of young people descend on sunny Southern California to redefine truth through all means of liberation.

"Inadvertently, Laurie meets a charismatic street preacher and a pastor who open the doors to a church to a stream of wandering youth."

In an interview with USA Today about his role in the movie, Grammer admitted to sometimes being angry with God and wrestling with his faith but said that it had sustained him through many personal tragedies.

"I've had hiccups. I've had some tragic times. I have wrestled with those and worked my way through them, sometimes rejecting faith, sometimes rejecting God even, in a period of being pretty angry about it. Like, 'Where were you?' That kind of thing," he said.

"But I have come to terms with it and have found great peace in my faith and in Jesus.

"It's not cavalier - Jesus made a difference in my life. That's not anything I'll apologise for."

He told USA Today that Jesus Revolution is a "really uplifting" and "good" movie.

"My wife and I saw it together. She was just dissolved in tears and said, 'It's the best thing you've ever done,'" he added.