The British Foreign and Commonwealth Office said opposition groups in Bahrain have called for more public demonstrations in Manama.
The warning said it expected protests in the country to be ongoing. Dozens of people were killed during a 2011 uprising against the Sunni-led monarchy and human rights groups have said demonstrations have been a common occurrence.
The British warning said Friday protests may include attempts to block traffic, the use of Molotov cocktails and explosive devices.
"As a result there could be clashes between government security forces and protesters," the warning said.
There were no reports of violence Friday from the official Bahrain News Agency.
The British government issued a similar warning one week ago. BNA reported then that four police officers suffered minor injuries in a bomb attack described as an act of terrorism.
Bahrain has been criticized for its human rights record. The government maintains it is committed to reforms outlined by a independent panel that reviewed its response to the 2011 uprising.