Shepard, 35, proposed over the holidays, a source tells Us.
Bell, 29, debuted her ring on the red carpet of the Grammys Sunday night.
The couple first stepped out publicly in January 2008.
Bell detailed her perfect date night with Shepard in the November issue of Women's Health.
"There is almost nothing, barring a natural disaster, that I would let eat into my time at home, playing Scrabble with Dax or talking to my girlfriends," she said.
She joked that they were competitive while filming romantic comedy "When in Rome," currently in theaters.
"We were trying to one-up each other," she said. "That's what we do at home, too. It's like, 'Wait, watch me do this funny bit.' 'No, watch me do this funny bit!.'"
The secret to their relationship?
"I've learned the necessity for healthy communication. How important it is to talk about your deepest, darkest fears and feelings," she says. "Your partner should hear your most embarrassing insecurities, because once you say them out loud, you've created a safe zone."
And "a snuggle party can fix anything -- it's true," she added.