An interior ministry spokesman quoted by official media described the victim as a British resident of Saudi Arabia, but did not give his name.
He said the incident was under investigation.
An AFP reporter witnessed the victim being taken away by ambulance citing witnesses saying the man was killed outside a supermarket on Khrais road in the eastern sector of the city at around 5:00 pm (1400 GMT).
Private security guards at the scene also said the man was British.
The motive for the killing is still unknown and no one has yet claimed responsibility for the attack.
Saudi authorities have stepped up security efforts in the kingdom in an attempt to ensure the security of expatriates.
Attacks on westerners in Saudi Arabia have increased since the US invaded Iraq and Israel has intensified its attacks on Palestinians.