The girl, Suhana, was kidnapped on Sunday by two men with weapons and two women wearing burqas, she told police. Police did not release her last name.
She was on her way to school when they seized her and drugged her, she said in a news conference broadcast by CNN affiliate GEO TV.
Suhana was driven to the Darra Islam checkpoint in Pakistan's Lower Dir district and "told to detonate a suicide vest that the abductors had put on her," district police officer Saleem Marwat told CNN.
"Instead of detonating the jacket, after getting out of the car, the child started shouting and running towards the paramilitary frontier corps soldiers stationed at the... post," the officer said.
She was arrested, her explosive vest was taken off and she was placed in custody, he said.
The Pakistani Taliban have used children as suicide bombers before, but there have been few cases, if any, of children as young as nine.
Pakistani and U.S. officials alleged in 2009 that a top Taliban leader in Pakistan was buying and selling children for suicide bombings.
Pakistan's military released a video showing children going through exercises in training for their attacks.
Taliban leader Baitullah Mehsud then sold the children to other Taliban officials for $6,000 to $12,000, Pakistani military officials said.
Meshud was killed in an apparent U.S. drone strike in August 2009.
As recently as April, a Pakistani teenager named Umar Fidai said teens were being trained in the country's tribal region to stage attacks.
Fidai was arrested alive after the suicide bombing at a Sufi shine in April killed at least 41 people and wounded more than 100. The blast occurred in Dera Ghazi Khan in Punjab province.
Fidai said in TV interviews he got suicide bombing lessons for six months, including training to use pistols, grenades and a suicide jacket. He said an Afghan Taliban leader named Mullah Sangeen was in charge of the training camp.