Andrews' publicist said that Andrews and actress Barbara Hershey were separated for a "brief period" last year, during which Andrews had an encounter with another woman. He recently learned that he is the father of her baby boy.
"I have every intention of assuming appropriate responsibility for the child," Andrews said Friday in a statement released to The Associated Press.
Andrews said he and Hershey have worked things out and remain committed to their relationship.
The British-born Andrews, 35, plays Sayid Jarrah, a former member of Iraq's Republican Guard, on ABC's "Lost." He is currently nominated for a Golden Globe for supporting actor in a series, miniseries or movie.
Hershey, 57, has appeared in films including "Lantana," "Breakfast of Champions" and "Falling Down."