Kenyan Coast Regional Police Commander Larry Kieng confirmed the attack at Maleli on Friday, saying security officers are pursuing the attackers.
Kieng said the attackers torched three houses in the same village.
This follows a series of attacks in the region.
On August 2, three other locals were killed after suspected al Shabaab militants attacked a passenger bus at Nyongoro area in Witu, Lamu county.
"The militants attacked and butchered the locals".
The forest is used as a recruitment and training ground for Al-Shabaab members.
A similar incident was reported in the area after Al Shabaab militants ambushed a passenger bus and a auto at Nyongoro area in Witu, Lamu County.
A major operation that has brought together KDF and the different police units is ongoing in the area but the onslaught by the terror group is yet to stop.
The ministry said in a tweet that the 12-hour curfew, from 6:30pm (1530 GMT), affects parts of Lamu, Garissa and Tana River and is to be in place for the next three months.
The al-Qaeda-linked al-Shabaab has vowed retribution after Kenya sent troops across the border to Somalia in 2011 to fight the group, which a year ago became the deadliest Islamic extremist group in Africa.