Two vehicles laden with explosives were seized during the raids on Sunday in the southern city of Kandahar, which has suffered a spate of attacks in recent months, Asadullah Khalid, the governor, said.
He said the nine were suspected Taliban members and allegedly planned to carry out an unspecified number of attacks against US-led multinational forces and government targets.
The governor declined to identify the detainees or give other details about the raids.
The arrests came the same day Afghan security forces set up checkpoints on all roads leading into Kandahar and started searching vehicles entering and exiting the city.
Six other checkpoints were set up inside the city, causing massive traffic jams.
Earlier this month, Hamid Karzai, the Afghan president, dispatched police reinforcements to Kandahar to crack down on fighters.
Since late September, some 20 human bombings have wracked Kandahar and other southern provinces. Prior to that, such assaults were relatively rare. The new tactic has reinforced fears that insurgents are mimicking tactics seen in Iraq.