Sunday's attack in Lawanti village, in the Jere area of Borno state, again underlined the threat posed by the group to people outside heavily-fortified towns and cities.
Mohammed Asheik, from the Civilian Joint Task Force assisting the military with security in the northeast, said: "Our people went to the farm to work.
"Seven Boko Haram on two motorbikes met them and slaughtered two, then killed the other four. They killed six people in all."
Asheik's account was supported by Jidda Ahmed, who said his elder brother, Musa Jidda, was "shot and beheaded" as he tried to flee.
Boko Haram rarely claims attacks but the method is in keeping with tactics seen elsewhere in the long-running conflict.
Attacks on isolated rural communities have been a feature of Boko Haram's Islamist insurgency in the remote region in recent months after the end of the annual rainy season.
Nigeria's military, with help from regional allies, have succeeded in pushing the jihadists out of territory captured in 2014 and 2015.
But farmers have been forced to try to resume their work to help alleviate chronic food shortages that have left hundreds of thousands starving and dependent on food aid.
Fields and farms have been blighted by eight years of conflict, with locals unable to sow or cultivate crops.
At least 20 000 people have been killed and more than 2.6 million others made homeless since the fighting began in 2009.