Police were checking vehicles when a man walked up and detonated a suicide vest, they said.
Police officers are also thought to be among the dead.
Afghanistan’s eastern provinces, some of which border Pakistan’s restive tribal areas, have seen an increase in militant attacks in the past year.
“The aim of the attacker was to target both police and civilians,” provincial police chief Gen Sardar Mohammad Zazia told the Associated Press news agency.
“Unfortunately, the majority of the victims are civilian,” he said.
No group has said it carried out the attack, but Taliban militants frequently target police checkpoints.
The attack comes a day before a Nato summit in Chicago that will discuss Afghanistan’s security transition, as local forces prepare to take over from foreign troops by the end of 2014.
Meanwhile, Afghanistan’s main human rights organisation says that local police in some areas are making things worse rather than better.