The incident occurred in Turabah, about 100 kilometres (62 miles) east of Taif in the kingdom’s southwest.
The official Saudi Press Agency said 150 people suffered food poisoning “because of eating meals” at the restaurant.
The online newspaper Sabq, which is close to authorities, said 175 people fell ill after eating shawarma sandwiches, a Middle Eastern staple.
Mecca region governor Prince Khaled al-Faisal ordered an investigation, “with the maximum penalties for the perpetrators of the poisoning incident,” SPA said.
It added that 45 patients “are under surveillance” at Turabah hospital and 32 at other medical facilities.
Saudi Arabia has invested heavily in its medical system.
About 15 percent of this year’s budget is allocated to health and social development spending, including for the setup of hospitals and healthcare centres “in all the regions across the kingdom,” the budget said.