The Thursday evening blast struck in the village of East Akar, one of a string of suburbs of the capital that have seen persistent unrest since the Gulf state's Sunni minority rulers crushed Shia-led protests for a constitutional monarchy and an elected prime minister in 2011.
Most of the disturbances have involved demonstrators throwing petrol bombs at police, who have deployed heavily in Shia areas as authorities have carried out an intensifying crackdown on the majority community's leaders.
Bahrain jails 19 Shias for attacks on police
A police statement carried by the official BNA news agency gave no other details of the Thursday explosion.
A court's decision last this month to strip the kingdom's Shia spiritual leader, Sheikh Isa Qassim, of his citizenship sparked protests in his home village outside Manama.
The authorities' crackdown has drawn criticism from key ally Washington, which has called repeatedly for reform and reconciliation with the Shia-led opposition.
Tiny but strategic Bahrain lies just across the Gulf from Shia Iran and is connected by a causeway to Sunni Saudi Arabia. It is the home base of the US Fifth Fleet.
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