State oil company Saudi Aramco said none of its employees had been injured but gave no further details.
Diplomatic spat: Saudi-Iran crisis widens as Kuwait recalls envoy
SPA said the men had stopped the bus in the district of Qatif, the home of prominent Shia Muslim cleric Nimr al-Nimr, who was executed on Saturday with 46 other men.
Nimr's execution has angered Shias across the Middle East and caused a major diplomatic row between mainly Shia Iran and Saudi Arabia's conservative Sunni monarchy.
Social media showed pictures and footage of the bus burning.
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