At around 2:10 a.m., on Saturday, police said the man was in his car at the gas pumps at a convenience store in the 8900 block of Winkler Drive.
The victims told police that while sitting in the driver's seat, an unknown man abruptly opened his door, pointed a handgun, and demanded his things.
The suspect then allegedly grabbed a bag inside the car, along with the man's wallet, and a necklace, police said.
Officials said the suspect got into a gray Nissan Altima and fled the scene.
The suspect is described as a Black man, wearing a black hat, white shirt, and black pants.
Anyone with any information regarding the robbery is urged to contact Crime Stoppers directly at 713-222-TIPS (8477). Information leading to the arrest and/or charging of the suspect may result in a cash payment of up to $5,000.