Salim Saleh, spokesman for the provincial governor in Logar, said eight others were wounded in the attack which took place in Puli Alim, the capital of the province.
The head provincial judge, Haqiq Rahman, and the head of the city's appeals court, Abdul Rahman, as well as two other judges were among the wounded. Four civilians were also injured, he said.
No group claimed responsibility for the attack in Logar. The Taliban frequently use roadside bombs and suicide attacks against Afghan and NATO forces and government offices across the country.
In Kunar province, on the border with Pakistan, the bodies of three health workers involved in vaccinating Afghan children against polio were found late Saturday, almost two weeks after they went missing in Ghaziabad district, the governor's spokesman Abdul Ghani Musamim, said.
"A vaccinator and a district health supervisor were kidnapped with their driver 12 days ago," he said, according to the Associated Press.
Polio, a debilitating disease that is prevented with vaccinations in the form of drops for small children, is endemic in Afghanistan and neighboring Pakistan.
Polio vaccinators are regularly targeted in areas of both countries outside government control, slowing progress in wiping out the disease.