According to witnesses, the attackers stopped motorists on a highway in Borno state and shot and hacked them to death.
Earlier, a media report put the death toll over 10, while blaming suspected members of the Islamist sect Boko Haram for the incident.
Nigerian military on Tuesday killed 40 Boko Haram fighters
It's the latest attack in a region which has suffered violence from the militant sect of Boko Haram. The group had suffered a deadly blow only days ago in the northeastern state of Borno.
On Tuesday, the Nigerian military had announced having killed 40 Boko Haram fighters during security operations.
The Boko Haram sect seeks to enshrine the Islamic sharia law into the constitution and the recent attack seems to be a revenge taken on the Nigerian military.