The bomb was planted in a shop next to a street market in the city of Dera Ismail Khan, scene of an explosion Saturday that killed at least seven people, including four children.
A doctor at a hospital in Dera Ismail Khan told Reuters five people were killed and 70 wounded in Sunday's blast. "There is a lack of ambulances and not enough hospital beds," he said. "People brought many of the injured to the hospital on rickshaws."
Dera Ismail Khan is a stronghold of Sunni militant groups who view minority Shias as non-believers.
On Wednesday night, a suicide bomber killed at least 20 people at Shiite processions in Rawalpindi. That attack occurred hours after two back-to-back bomb blasts near a Shiite gathering in Pakistan's commercial hub Karachi, which killed three people and left many others wounded.
More than 300 Shias have been killed in Pakistan so far this year in sectarian conflict, according to human rights groups.
Tens of thousands of police have been deployed around Pakistan as Sunni militants warn of further attacks.
The government has shut down the mobile phone network in Karachi, Quetta, and some other cities as a part of security measures for the weekend, which marks the culmination of the holy month of Muharram, a key event in the Islamic religious calendar. particularly for Shias.
Interior Minister Rehman Malik also announced more curbs for Saturday and Sunday saying authorities had also received requests from Punjab province to suspend mobile phone services in 14 major cities and towns including Lahore, Rawalpindi, Faisalabad and Multan, news agencies reported.
This is the fifth time in 2012 that the government has opted to suspend mobile services because of security measures.
Pakistani authorities believe militant groups such as Lashkar-e-Jhangvi, which has close ties with al Qaeda, are stepping up attacks on Shias, in a bid to destabilize the nation and establish a Sunni theocracy. The minority Shias account for up to 20 percent of Pakistan’s 180 million people.