The attack on a police truck took place on Monday in the eastern coastal county of Lamu, which borders Somalia and has been hit by a wave of attacks by the al-Qaida linked group.
"Five people were killed in the attack, including a mother and her child," Lamu police chief Chrispus Mutali said, adding that five others were wounded in the attack, AFP reported on Tuesday.
All those killed were reportedly civilians who had been given a lift by the police, while the officers escaped unharmed.
Shebab militants have recently been blamed for a string of security incidents in the Lamu area, including attacks on passenger buses and a failed raid on a military base last month.
The militant group is believed to have fighters operating in the area's Boni forest.
In mid-June 2014, close to 100 people were killed in a series of armed assaults on the town of Mpeketoni and surrounding villages in Lamu county.
These attacks, close to the once-popular holiday island of Lamu, led to a collapse in tourism on Kenya's coast after foreign governments warned their nationals against travel to the area.