The memorial included a slide show, remarks from friends and a screening of the 1999 film "The Green Mile," for which Duncan was nominated for an Oscar, NBC Los Angeles reported.
Duncan's casket was closed during the 4-hour memorial service.
Duncan, 54, died on Sept. 3 at Cedars-Sinai Medical Center in Los Angeles, the Los Angeles Times reported.
He had suffered a heart attack in July, his publicist, Joy Fehily, said.
A private memorial service for friends and family is scheduled for Monday, KTLA-TV, Los Angeles, reported.