The pair -- who played lovers in 2001 movie "Sweet November" and starred together in "The Devil's Advocate" -- stunned onlookers with their intimate embrace as they left a Beverly Hills restaurant Monday night.
A fellow diner at upscale eatery Bouchon revealed that Theron, 34, and Reeves, 45, enjoyed each other's company and seemed in no hurry to end their date, tasting several red wines before selecting a bottle and indulging in several snacks before starting their meal.
"Keanu and Charlize were having a great time," the onlooker told website HollywoodLife.com.
"They were constantly laughing, almost disrupting other tables with how loud they were. They were wrapped up in each other's conversation and having a great time together."
Theron has been single since splitting from long-term partner Stuart Townsend in the New Year, while Reeves -- whose partner Jennifer Syme died in a car accident in April 2001, two years after their baby was stillborn -- enjoyed a brief romance with actress Cameron Diaz earlier this year.