An army patrol came under attack late on Wednesday near the village of Dalfing in Rukum district, about 400km west of the capital, Kathmandu.
In the ensuing fighting, the army killed at least 60 rebels, Major Sushil Dahal at the Royal Nepalese Army headquarters in Kathmandu said.
Details were still sketchy because the fighting was in a remote part of the country which is mostly controlled by the rebels.
No casualties were reported on the army side.
Last week, the army said it was able to repel a major rebel assault on one of its bases in the same district, killing at least 152 fighters.
Hundreds of rebels attacked the base near the Khara village on 7 April. Three soldiers also died.
The region where the fighting occurred is believed to be a rebel stronghold and government forces have been largely confined to their bases in the area.
The rebels began fighting to overthrow the monarchy and establish a communist state in 1996. More than 11,500 people have been killed in the insurgency.