The owner of the gas station said a man mounted the device while his wife distracted the manager.
WATCH: CA store owner protects tourist after brazen attack
The manager later noticed that the credit card machine looked different and took it off before any customers used it, the owner said.
The manager also checked all of the station's gas pumps for skimmers. No other devices were found.
Covina Police Department detectives are investigating and searching for the suspects involved.
MORE: Video shows owner torching his own restaurant: Investigators