
The incident, in which two others were injured, occurred in the southern province of Jazan at about 2:00 pm (1100 GMT), ministry spokesperson General Mansour al-Turki told AFP.
"This is a criminal act," said Turki, adding that one suspect had been arrested.
He was unable to immediately confirm how the victims were killed but state television reported it was a shooting.
The identity and motive of the suspect were unclear.
The incident occurred in the remote community of Ad Dair, several kilometres from the Yemeni border.
Jazan and other southern border districts have been shelled by rebels in Yemen since last March when a Saudi-led coalition began air strikes and later ground operations to halt the advance of the Huthi rebels there.
Suicide attack kills four in Saudi city

More than 90 soldiers and civilians have been killed in shelling and skirmishes in the Saudi border region.
Elsewhere in the kingdom there have been mass shootings and bombings claimed by the Islamic State group against the Shia minority community. IS has also targeted the security forces.
But criminal mass shootings are rare in Saudi Arabia.
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