At least three people were killed in an attack on a mosque in Saudi Arabia's eastern governate of al-Ahsa on Friday, the media reported.A suspect in the attack has been reportedly arrested, sources said.Eastern regions of Saudi Arabia were on alert after ISIS claimed two attacks on Shia mosques in 2015.In August, at least 15 people were killed in an attack on a mosque in southwest Saudi Arabia.In May, a suicide bomber blew himself up during Friday prayers at a mosque in the village of al-Qadeeh in eastern Saudi Arabia, killing at least 21 and injuring 81 others.