The suicide bomber blew up an explosive vest at noon when he was surrounded by a procession of pilgrims, Xinhua reported.
The attack took place near the city of Sa'diyah.
The victims were taking part in Ashura commemoration rituals, which mark the death of Imam Hussein, who was killed in 680.
Thursday's attack comes after a series of bombings killed 22 pilgrims and police officers Wednesday.
Notable deaths of 2014 [PHOTOS]
Ebola health workers killed in Guinea