Larter, 38, who wed McArthur, 37, in 2009 and has a two-year-old son with him, revealed the news during an appearance on a chat show.
The blonde beauty said that it has not been easy trying to hide her pregnancy, especially since she has been working on a new action TV series, 'Legends'.
"I've been trying to hide it (the bump) as much as I can. And you know, when you're in the public eye, it's really scary in the beginning.
"I was still shooting my spy drama, 'Legends', where I have to be a covert spy and a spy in my real life too. So I'm wearing blazers and doing everything you can do to distract as the bump is growing," she said.