The predominantly Shia Muslim region has suffered unrest since early 2011, with protesters complaining of discrimination by the Sunni monarchy.
It has also been the scene of attacks by Islamic State militants this year.
In October, a gunman from a local affiliate of the Sunni jihadist group shot and killed five people at a Shia meeting hall in Saihat before being shot dead by police.
The interior ministry said an investigation into Wednesday`s attack was under way.
More about:
