The attackers, who included women, detonated their explosives in the Muna district, police said.
No group has said it was behind the attack. However, the Islamist militant group Boko Haram has carried out many attacks in Maiduguri, in Borno state.
It frequently uses female suicide bombers to launch attacks.
The first blast happened at about 17:00 GMT, close to a group of people conducting evening prayer, killing seven, state official Bello Dambatta said.
Another attacker detonated explosives inside a house and the other two blew themselves up before reaching their targets, he added.
Boko Haram has been fighting to set up an Islamic state since 2009.
A report published by US anti-terrorist researchers earlier this year said it is the first insurgency in history to use more women suicide bombers than men.
Thousands of people have been killed and millions forced to leave their homes by Boko Haram violence in recent years. (Courtesy BBC)