Security forces gunned down two NDFB ultras in Kokrajhar district on Saturday.
The ultras, holed up at Sapkata area, were shot dead by a joint team of police and army, official sources said.
One of the militant was identified as Abani Basumatary (25), while the other's identity was not yet known, they said.
On Saturday two NDFB ultras, including one who was involved in the October 30 Assam serial blasts last year that left 90 persons dead, were killed by security forces in nearby Basbari area.
In stepped operation against the NDFB, nearly 40 ultras have been killed in the last three months, police said.