The Naxalite fired at the policemen when they were returning from a patrol in a jeep at Lajrai More late on Monday night, police said on Tuesday.
Two home guards and the civilian driver were injured in the attack.
Those killed included Assistant Sub-inspector Narayan Mandal, hawaldar Akhilesh Paswan and home guard Gandru, police said, adding it was not a landmine blast as initially reported.
R K Mallick, spokesperson of Jharkhand police said, "The patrolling party had gone to inspect a road construction site and the Maoists were laying ambush in that particular area and the party came under fire. We have lost three persons".
The rebels also looted two guns and torched the jeep. Sources at the Tandua police station, under which the incident took place, earlier said it was a landmine blast.
The incident comes close on the heels of the Maoists abducting a district collector and a junior engineer from Orissa's Malkangiri district.
The two were released after the Orissa government conceded to some of the demands of the rebels.
