Officials said the mourners' procession was passing through its traditional route when a roadside bomb exploded in Mirazai town killing two mourners and injuring eight others.
Elaborate security measures, including monitoring by helicopters and drone-mounted cameras, are in place across the country to provide security to Shia Muslims during the holy month of Muharram.
An official of the interior ministry said that mobile phone and internet services were suspended in several cities and towns as militants use them to communicate and carry out remote-controlled blasts.
Thousands of police and paramilitary security personnel have been deployed across the country. Army troops are also deployed in sensitive areas.
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An official of Punjab police said that the authorities have also arrested dozens of activists of anti-Shia groups in the province.
So far mega processions in Karachi, Lahore, Multan and Rawalpindi remained peaceful.
In Karachi, the country's biggest city, more than 25,000 security personnel are providing security.
Special arrangements have been made in the garrison city of Rawalpindi after last year's clashes between Shia and Sunni groups which prompted authorities to clamp curfew in the city.
Prime Minister Nawaz Sharif in his message on the occasion urged calm and respect for all.
Shias constitute about 20 per cent of Pakistan's population and they are regularly attacked by Sunni extremists who consider them to be heretics. The processions make them more vulnerable to attacks.