The explosion on Wednesday took place in Rukubi, a village on the border between Nasarawa and Benue states, a region known for ethnic and religious violence.
"We now have approximately 40 people that were killed," Nasarawa Governor Abdullahi Sule told reporters on Thursday.
"The rumor earlier was that the air force carried out the bombing but right now we understand that there was no air force plane that flew (above) the area," Sule said on Arise News television late Wednesday.
"Instead it was a drone that flew (above) the area and dropped the bomb," Sule said, without specifying who was operating the aircraft.
An umbrella group representing herders had said the explosion was caused by a Nigerian military jet.
"We all know it is only the military that possess jets to carry out aerial strikes," Lawal Dano of the Miyetti Allah Cattle Breeders Association of Nigeria said Wednesday, calling for a government investigation.
Nigeria's air force spokesman did not respond to AFP requests for comment.
There have been accidental airstrikes on civilians by the military in the past in northern Nigeria, where troops are fighting jihadists and criminal gangs.
In September 2021, officials said an accidental Nigerian military airstrike on a village in Yobe state killed at least nine civilians.
The air force said its jet had been pursuing a group of jihadists in the area.
In January 2017, at least 112 people were killed when a jet struck a camp housing people displaced by jihadist violence in the town of Rann, near the border with Cameroon.
The Nigerian military blamed a "lack of appropriate marking of the area" for that bombardment in a report issued six months later.
In central Nigeria, herders and farmers have been clashing over grazing and water rights for decades, but the violence has worsened in recent years after some herders joined criminal gangs that raid villages.
The conflict has also taken on an ethnic and religious dimension, with most herders being Muslims while farmers are largely Christians.
Last Thursday, nine people were killed when suspected herders opened fire outside a camp for people displaced by attacks near Makurdi, the capital of Benue state, according to local officials.
Security is a major issue in Nigeria ahead of next month's elections to replace President Muhammadu Buhari, a former army general.