Credit: Jcgo/Juan Garces/Splash News Online

Someone's been working out!

Cameron Diaz showed off her taut, toned bikini body Sunday in South Beach, Florida. The actress, 38, flaunted her washboard abs, strong biceps and long legs in a bright yellow bikini.

According to an observer, the Bad Teacher star was "chatting with friends, running into the water and having a blast." She "even took time to meet fans on the sand."

Considering her beau Alex Rodriguez is a professional athlete, it's no surprise that Diaz takes fitness so seriously. So what's her favorite way to stay in shape? In an interview with Self magazine, she said that sex is "the best exercise!"

Tell Us: What do you think of Cameron's bikini bod?