Last year, Aftab Ahmed Khan Sherpao, a former interior minister, survived two separate suicide bomb attacks in Charsadda that killed scores of people.
The ANP is a secular ethnic Pashtun group competing in the legislative elections on February 18.
Elections scheduled for January were postponed after Benazir Bhutto, a former prime minister, was assassinated on December 27.
In the south of the country, tens of thousands of Bhutto's followers rallied on Saturday in the town of Thatta, chanting "democracy is the best revenge".
Police estimated that a crowd of more than 100,000 people had gathered as the late opposition leader's Pakistan People's Party (PPP) re-launched its election campaign.
"She wanted to change the system and that is why the system has killed her," Asif Ali Zardari, Bhutto's widower and the de facto party leader, told supporters.
"The system is her killer, but she knew that even if she lost her life, people like you and me would complete her mission and take revenge."
Bhutto's supporters have accused Pervez Musharraf, Pakistan's president, of being partly responsible for her death on the grounds that he did not assign her enough security.
The government has blamed an al-Qaeda-linked tribal leader, Baitullah Mehsud, who is based in the South Waziristan region on the Afghan border, for Bhutto's killing and many of the other recent attacks across the country.
Mehsud, the most wanted man in Pakistan, has denied the charge.
Saturday's attack in Charsadda also comes at a time when Mehsud has declared a unilateral ceasefire nationwide.
Hyder said: "Tonight, the big question is who carried out the attack and why, and why so close to what is being considered the country's most crucial election in its history."
Security analysts fear more attacks will be launched in the run-up to the vote in an attempt to further destabilise the country.
Some Pakistanis fear that Musharraf, whose allies look set to perform poorly in the vote, might use violence as an excuse to postpone the elections again.
Separately, police used water cannons and tear gas to break up a protest by hundreds of lawyers who tried to march to the home of Pakistan's deposed chief justice in the capital, Islamabad.
|Seven people were injured as police dispersed|
the protesting lawyers [Reuters]
Iftikhar Chaudhry was dismissed in November when Musharraf imposed emergency rule citing rising militancy and a meddling judiciary.
He has been kept under house arrest since then.
Seven people including four policemen were injured in Saturday's protest, a city official said.
Lawyers have been at the forefront of a campaign against Musharraf since March, when he first tried to dismiss Chaudhry.