It took place late on Wednesday night, according to a security source quoted by the Reuters.
Local MP Bulu Mammadu told the BBC that the victims included women and children who had been shot dead in two different villages.
Boko Haram is based in Nigeria but is being tackled by a multinational force, including soldiers from Niger.
On Monday, there was a suspected Boko Haram suicide attack in Chad, which is also supplying soldiers to the multinational force.
Chad responded to that attack with air strikes on suspected Boko Haram positions.
In Niger, Mr. Mammadu said that, as well as killing people, the militants had burnt down several houses in the two villages of Lamina and Ungumawo in the Diffa region, close to Nigeria's border.
But on his Twitter handle on Thursday, President Muhammadu Buhari assured Nigerians and their neighbours that the Boko Haram insurgents would soon be defeated.
"I mourn every single death of a Nigerian as a result of terrorism. That is why security is my number one priority.
Our efforts to strengthen security cooperation with our neighbours and adjust our own response to Boko Haram will yield results very soon. Our resolve and capacity to end terrorism is much greater than the threat we face. Nigeria will prevail," Buhari said.
Boko Haram first attacked Niger in February when the government said it repulsed an attack, killing more than 100 of the group's fighters.
Since being sworn in last month, Nigeria's new President Buhari has pushed ahead with plans to beef up the multinational force which will be made up of 7,500 troops.
On Monday, the United States of America's government, at the 25th African Union Summit pledged the sum of $5 million to back Nigeria and its neighbours in their fight against Boko Haram.
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