Without a Trace's Poppy Montgomery Pregnant

Without a Trace actress Poppy Montgomery and her boyfriend, actor Adam Kaufman, are expecting their first child, she tells PEOPLE exclusively.

"It's so crazy. I'm like: Oh my god! I can't believe it," Montgomery says.

The baby is due in December.

Montgomery, 32, who plays FBI Agent Samantha Spade on the CBS drama, met Kaufman about three years ago on the Mexico set of the independent film Between. Kaufman has also appeared on Law & Order and Dawson's Creek.

Montgomery says she and Kaufman talk about marriage "sort of peripherally" but that "it's not a huge priority right now."

"We're together," she says, "and that's all that really matters."