The National Party billboard featured Tauranga MP Simon Bridges and Bill English, but it was the Prime Minister's face that was burned off.
"They have clearly gone for his [Bill's] face," Miss Harborne said.
Miss Harborne lived with her three children and said she was a little concerned the fire happened so close to her home.
"It concerns me because you think about how close they are to the houses," she said. "It does make me cautious especially since our houses are so old."
The billboard had since been replaced with a new sign of the Prime Minister's face.
A police spokeswoman said the fire was under investigation to determine if the blaze was possible arson.
"Police are looking for witnesses to the event and are urged to come forward if any suspicious activity was seen on Devonport Rd last Saturday night [September 2]."
The damage comes about a month after the Simon Bridges' face was cut out of an election sign on Totara St in Mount Maunganui and was one of about five other signs to be vandalised.
The faces of Act Party leader David Seymour, Tauranga MP Simon Bridges and Prime Minister Bill English have also been cut out of election signs erected in Matua and Mount Maunganui.
Mr Bridges could not be reached for comment.
A Tauranga City Council spokeswoman said the council had not received any complaints about vandalised political signs.
She said the council had received complaints regarding the incorrect placement of between 5-10 election signs.