The couple, who co-star on TV's "Ghost Whisperer," have dated for less than a year.
The New York Post said Kennedy proposed to Hewitt on-stage during his stand-up comedy show at the Laugh Factory in Long Beach, Calif., last weekend. The newspaper also said the actress agreed to be his bride.
"There is no truth to the report," Hewitt's representative told Usmagazine.com.
Millions of Getty images now available for free via embed tool
NBC reportedly holds celebs hostage to Jimmy Fallon's show