Five people were killed in a raid on a village outside Maiduguri, a stronghold of Islamist militants Boko Haram.
In a second attack, gunmen killed two people, including a policeman, and burnt down government buildings in Maiha, on the border with Cameroon.
No group has claimed responsibility for the attacks.
The Nigerian military said it had arrested three people and seized weapons following the attack outside Maiduguri.
A school teacher in the village told the Associated Press that gunmen had gathered people into a group before massacring them. The teacher said 15 people had died in the attack; many had had their throats slit.
Violence linked to the Boko Haram insurgency – a group seeking to impose Islamic law on the country – has claimed hundreds of live in 2012.
Six people died in an attack on a church on Christmas Day, while seven people were killed on Wednesday in Maiduguri, the city where Boko Haram launched its campaign in 2009.
Nigeria is divided between a mainly Muslim north and a Christian south.