The attack on Tuesday in the central province of Uruzgan is the latest in a wave of violence in the run-up to the parliamentary and provincial council polls that has left more than 1000 people dead this year.
Governor Jan Mohammad Khan said the fighters stopped a vehicle with seven people inside in Gizab district.
"They searched everybody, and found an official document, a car registration for election day, on one of them. Then the Taliban killed the seven people," Khan said.
In a separate incident on Tuesday, Taliban fighters hanged an intelligence official in the southeastern province of Zabul, police said.
"A man named Hamid Allah who works for the district intelligence department was captured and killed by the Taliban. He was hanged," local police chief Ghulam Aidar said.
The Taliban have vowed to sabotage preparations for Afghanistan's first parliamentary elections for more than 30 years.
Six candidates have died in political violence since early July, when some 5800 Afghan men and women signed up to run for office.
Last week, Afghan police found the bodies of a parliamentary candidate, a district chief and three others kidnapped by Taliban rebels in the southern province of Kandahar, the stronghold of the former government.
Afghanistan's elections are set
Two other election candidates escaped attacks on Tuesday.
The car of one was blown up by a roadside bomb in the eastern province of Nangarhar while the vehicle of another came under fire in Takhar province, to the north.
However, officials said the victim of the second attack had links with the drugs trade and was likely targeted by rivals.
With violence continuing in the run-up to the polls, President Hamid Karzai on Tuesday urged the international community and the US-led military coalition to rethink their strategy for fighting terrorism in the country.
The New York Times reported on Wednesday that top US military officials are considering cutting the 20,000-strong force by as much as 20% by next spring.
Meanwhile Nato defence ministers will continue efforts at talks in Berlin on Wednesday to ease strains over how to expand the alliance's separate peacekeeping force in the war-torn country.