The complex attack in the city of Khost was launched early in the morning, and has wounded 14 security personnel and nine civilians.
A gun battle near the base was ongoing, an AFP correspondent reported.
The car bomb was detonated at the gate of a special police forces base in Khost city, a security source said.
After the blast a group of attackers tried to enter the base compound resulting in a gun battle with security forces, Afghanistan's interior ministry spokesman Tariq Arian told reporters.
Four attackers have been killed while two more were still fighting, Arian said.
Khost provincial health official Gul Mohammad said women and children were among the wounded.
No group has so far claimed the attack on the base.