Najma Hanif was gunned down by the assailants inside her house in posh Hayatabad locality in Peshawar, provincial capital of Khyber Pakhtunkhwa, they said.
Hanif was a candidate of ANP for one of the reserved seats for women in the May 2013 elections from the area.
After the incident, police cordoned off the area and started search operation.
ANP chief Asfand Yar Wali Khan condemned the incident and expressed grief over losing an important party leader.
The victim's husband Hanif Jadoon and 16-year-old son were killed in a bomb blast in 2011.