Fields, 44, married Broadway actor Christopher Morgan, 37, in 2007. They are already the parents of 6-year-old Sebastian Alexander.
People.com said the former "Facts of Life" and "Living Single" star will officially announce her pregnancy on an episode of the chat show "The Real" next week.
"Sebastian and Christopher are very excited. We're very, very blessed," People.com quoted Fields as saying.
"It was planned. We've actually been trying for a couple years. We had gotten pregnant twice and [miscarried]. Chris and I were very blessed to really have one another, to have our family and friends and our God to really get us through that. ... If I'm encouraging to anybody ... it's not like I'm the poster child for over 40 and pregnant," she said.
"Funny enough, for a minute I thought I was getting pre-menopausal 'cuz certain things were starting to be irregular and then other symptoms started -- my memory and I was clumsier than normal which I couldn't even believe was possible. Then our son got sick with a stomach virus and I caught it. Chris said: 'No, babe, you're a little sicker than Sebastian. You need to go and get that checked out.' And I said, 'Okay.' They tested me and said: 'Oh, honey, you're not dehydrated. You're two months pregnant.'"
Fields did not say when her due date is.