Pakistan has undergone a surge in attacks by Taliban and al Qaeda-linked militants on government, military and Western targets over the last two years.
The attack occurred as the politician, Asfandyar Wali Khan, was receiving guests to mark the end of the Islamic fasting month at his home in Charsadda, said police officer Akhtar Ali Shah.
He said police challenged the bomber, who then blew himself up.
Shah said Khan was unhurt, but at least four people were killed and several others were injured.
A Pakistani security official told CBS News' Farhan Bokhari the attack "was probably in retaliation for last week's military attack on a Taliban stronghold in Bajaur," referring to a weeks-long operation to oust militants from a region along the border with Afghanistan.
"As we step up our attacks on the militants, we have to be prepared for bloodier retaliation," said the official, who spoke to CBS News on condition of anonymity.
Northwest Pakistan is the front line in the country's battle against the militants, who are also blamed for rising attacks on NATO and U.S. forces in neighboring Afghanistan.
Wali's Awami National Party competes with pro-Taliban religious parties for the loyalties of the region's ethnic Pashtuns. It has been sharply critical of Islamic extremists.
The grouping is also a key partner in the ruling coalition of pro-Western President Asif Ali Zardari.