Witnesses said gunmen in four speedboats attacked the home of former Bayelsa state deputy governor Peremobowei Ebebi at around 1130 GMT with improvised explosives, killing a private security guard.
Ebebi, who left Bayelsa months ago and was believed to be in the capital Abuja, could not be reached for comment.
Police confirmed the attack in Aleibri, a village about 40 km (25 miles) northwest of the state capital Yenagoa, but had no details on who the gunmen were or their motives.
"We have dispatched our men to the scene to take charge of the situation. From reports available to me, there was extensive damage to the residence," Bayelsa police spokesman Eguadoen Emokpae said.
Tensions have been high for months in Bayelsa due to a power tussle between Governor Timipre Sylva and Ebebi, who was impeached by the state legislature last month over allegations of corruption.
Ebebi fell out with Sylva shortly after the pair took office in 2008 and the rivalry has kept tensions high in one of Nigeria's most politically volatile states.
Bayelsa, the home state of President Goodluck Jonathan, is one of three main states in the Niger Delta, the heartland of Africa's biggest oil and gas industry.
Africa's most populous nation holds presidential and parliamentary elections early next year, including a vote for state governors and regional assembly members, and analysts fear the Niger Delta could be a flashpoint for political violence.
Friday's attack comes barely two months after a car exploded close to a guesthouse owned by Ebebi in Yenagoa, when there were no casualties nor any claim of responsibility.
An amnesty programme for militants in the Niger Delta has brought a year without any significant attacks on oil infrastructure in the region, helping the OPEC member to restore some production shut down by constant attacks.
The militants say they are fighting for a greater share of the region's oil wealth for local people, but much of the violence is carried out by criminal gangs who make money from kidnapping for ransom and stealing crude oil, and who have in the past been used by politicians to rig elections.
