The Argo star was seen knocking off the other vehicle's wing mirror while driving in Santa Monica at the weekend, TMZ reports.
However, he then wrote down his phone number and left it on the car's windshield, promising to pay for the damage.
"Hi, I knocked off your mirror!" he wrote. "Very sorry! Will cover everything - Ben."
Argo, which Affleck also directed, will pick up the prize for 'Ensemble Acting' at the Hollywood Film Awards later this month.
Meanwhile, Affleck recently suggested that he turned down the offer to work on the Daredevil reboot.
New! Digital Spy breakfast show - watch Anna Williamson discuss the day's biggest stories including The X Factor, Homeland and Leona Lewis: