"A car conveying six men, obviously Boko Haram fighters, exploded a few minutes ago just after passing by a security post in Fika," Abdurrahman Uthman, a local resident, told The Anadolu Agency by phone.
Yobe police chief Marcus Danladi has confirmed the blast.
"The people carrying the bomb inside a vehicle were the ones who died," he told reporters in Damaturu, Yobe's provincial capital.
"They came from one of the villages where the insurgents are hiding," added Danladi.
The police chief, however, stopped short of giving a death toll.
The incident comes barely one month after a spate of similar bombings in restive Yobe State.
Militants recently tried – but ultimately failed – to capture Damaturu in an early morning raid in which a number of locals, security operatives and militants were killed.
For the last five years, Nigeria has battled a fierce Boko Haram insurgency that has ravaged the country's volatile northeastern region and claimed thousands of lives.
2014 proved to be the insurgency's bloodiest year yet, with increasingly frequent attacks, higher death tolls and a deluge of displaced persons.
A seemingly emboldened Boko Haram recently stepped up its militant activity, seizing several areas of Nigeria's Adamawa, Borno and Yobe states, where it has since declared a self-styled "Islamic caliphate."