The three men, who were not carrying any weapons, were attacked with stones, knives and then shot dead in the Maoist stronghold of Ramechhap on Saturday, an army statement said on Monday.
The guerrillas have vowed to step up attacks on government forces and called for a nationwide general strike later this week to build pressure against King Gyanendra after he fired the government and assumed absolute power last month.
The rebels want to replace Nepal's constitutional monarchy with communist rule. More than 11,000 people have died in the nine-year revolt.
Call for strikes
Meanwhile, Nepal's main political parties said they planned to hold nationwide rallies next week to protest against the king's takeover last month and to mark the 15th anniversary of a mass movement that wrested absolute power from the monarchy and established democracy.
Nepalese civil society has
protested at Gyanendra's takeover
The demonstrations on 8 April will coincide with an 11-day general strike starting on Saturday that Maoist rebels called to protest against Gyanendra's actions.
Gyanendra sacked the government, declared emergency rule and suspended civil liberties on 1 February, saying his moves were necessary to defeat the escalating communist insurgency and root out endemic corruption among politicians.
Since the king's power grab, many politicians have been detained or driven underground.
The new monarchist government has released some opposition figures in recent weeks, but sporadic rallies to demand the return of democracy have failed to attract large numbers and have been quickly broken up by police.