Conflicting reports suggest at least 3 or 5 people were killed in the attack. Meanwhile, the country's Interior Ministry stated, as cited by Saudi state news agency SPA, that only two people had been killed.
Residents said security forces were exchanging gunfire with five "terrorists".
A suspect in the attack has been reportedly arrested, al-Arabiya reported.
RT MiddleEastEye "RT roridonaghy: Video shows Saudi security forces arresting one of the attackers who bombed and … pic.twitter.com/m3a3GYuJX8"— Iraq Intelligence (@IraqAnalysis) January 29, 2016
"Two suicide bombers attempted to enter Imam Rida Mosque in Mahasen neigborhood in the Ahsa province during the prayers. When security men stopped them, one blew himself up at the entrance of the mosque and there was an exchange of fire with the other," the Interior ministry spokesperson added, as quoted by the SPA news agency.
According to the Saudi Interior Ministry, Saudi police wounded and arrested the second suicide bomber, who was also wearing a belt with explosives.
No terrorist group has claimed responsibility for the blast.
Shiites in Saudi Arabia previously have been targeted by Daesh terrorists in the kingdom.
In August 2015, at least 15 people were killed in a suicide attack on Shiite mosque in southwest Saudi Arabia used by members of a local security force. In May, a suicide bomber blew himself up during Friday prayers at a mosque in the village of al-Qadeeh in eastern Saudi Arabia.
In early January, Saudi Arabia executed a prominent Shiite cleric Nimr al-Nimr.