The actress, who announced in November that she is expecting her first child with fiancé Dax Shepard, told Entertainment Weekly that she is due at the "end of spring".
"I'm not not pregnant," she joked. "When you see me, it will be obvious. This is without question the biggest transition I'll make in my life to date."
Bell added: "By the way, you kind of go brain-dead when you're pregnant. You're kind of in a dopamine phase. I'm kind of happy all the time, and dumb."
Bell also revealed that she has had "so much fun" filming the new season of Showtime's House of Lies, saying: "They are always trying to hide my pregnancy. I'm always hiding behind a box, or a purse."
She explained that the people working on House of Lies "love the fact that [she's] pregnant" and added: "We'll stop filming around February 12, around Valentine's Day, so I'll have a little bit of pregnancy time after."
Bell recently joked that her pregnancy has left her feeling like she weighs 400lb.