A rep for "The Big Bang Theory" star confirmed the news to Us Weekly, while an insider told the magazine: "It's only been three months but she knows Ryan is the one."
Sweeting reportedly popped the question on Wednesday. The couple made its red-carpet debut at a pre-Emmys party in Los Angeles on Friday, and the pair also attended Sunday night's ceremony together. Cuoco was considered one of the best dressed stars at the event in a maroon corseted dress.
Cuoco has dated British actor Henry Cavill and her sitcom co-star Johnny Galecki. She was once engaged to speech therapist Josh Rusnik.
The actress recently made headlines for her sister's appearance on music competition series "The Voice." Cuoco and her "Big Bang Theory" castmates also hit the news after they reportedly petitioned for raises. They reportedly make $325,000 an episode.
Sweeting was born in the Bahamas and won his first ATP World Tour singles title in 2011.