According to the Walnut Sheriff's Station, it happened just after noon on Saturday at the 99 Ranch Market store on Nogales Avenue.
The man and woman were loading groceries into their vehicle when two men ran up to them and began demanding the man's Rolex watch, deputies said.
Investigators said before the man could respond, one of the suspects pistol-whipped him and knocked him to the ground. The second suspect then pistol-whipped the woman he was with, authorities said.
The robbery was captured on video, which shows the woman screaming for help.
Violent robbery at Rowland Heights grocery store caught on video; 2 suspects at large
The suspects grabbed the watch and took off in a white Dodge Challenger with paper license plates.
According to the sheriff's station, the Rolex is worth about $60,000.
The suspects are being described as two men between 25 and 30 years old. They were seen wearing black hoodies and gray sweatpants and were both reportedly armed with semi-automatic handguns.
The Walnut Sheriff's Station said they're working in conjunction with the Temple Sheriff's Station after they've received reports of similar incidents over the past few days.
They believe the two suspects involved in Saturday's robbery may be the same two suspects involved in those incidents.
Anyone with information is urged to contact authorities.