The attack targeted the bus on the Khalifa bin Salman highway, the ministry said, adding that the militant group used a handmade bomb.
“Investigations are underway to determine the circumstances of this premeditated terrorist attack and arrest the group involved,” the ministry said in a statement on its website.
The incident was the latest in a series of attacks targeting policemen in the country where the U.S. Fifth Fleet is based.
The government blames the attacks on Shi‘ite militants it says are backed by Iran to destabilise the country, a charge Tehran denies.
This month, a blast wounded five policemen on Budaiya road, near Manama, while they were guarding a procession by Shi‘ite Muslims marking the annual Ashura festival, which commemorates the death of Prophet Mohammad’s grandson Imam Hussein some 1400 years ago.