The men were making the bombs in a tent in Dand district, said provincial government spokesman Zulmai Ayoubi.
"As a result of the explosion two were killed and three wounded," he said, adding that the toll may rise.
"They were killed by their own mines," confirmed Kandahar police chief Abdul Razeq.
Roadside bombs are the weapon of choice for the Taliban, whose 10-year insurgency has been largely focused on the southern heartlands of the country.
The United Nations says the first half of this year saw 1,462 civilians killed in the Afghan war, with insurgents responsible for 80 per cent of the deaths.