Police said another 22 people were taken to a hospital in Kohat from Hangu.
Interior Minister Aftab Khan Sherpao told CNN army and paramilitary troops were dispatched to the area to quell riots between Shiites and Sunni Muslims in a bazaar in the city of Hangu that broke out after the attack. A mob burned shops and government offices.
District administrator Ghani ur-Rehman said the ensuing violence had destroyed 60 percent of the town's bazaar.
No one has claimed responsibility for the attack, the BBC said.
Ashura marks the death of the Prophet Mohammed's grandson Imam Hussein more than 1,300 years ago, an event that led to the split between Shiite and Sunni Muslims.
The Shiites began the day with a traditional call to prayer and many took part in a ritual self-flagellation, with some cutting their heads with swords as they chanted.
Five people also died in Sunni-Shiite fighting in Afghanistan.