One of the victims was a four-year-old girl.
Another 30 people were injured in the accident.
The bus is reported to have rolled down a 100 meter long slope.
The accident occurred on Wednesday afternoon, local time, but it took several hours before the news of the crash reached due to it occurring in an inaccessible area.
The bus traveled between the city of Tayabamba to northwestern Trujillo, a distance of about 340 km.
A journey between the cities is estimated to take a full 14 hours due to poor road conditions.
Serious traffic accidents are common in Peru, among other things due to poorly maintained roads, high speeds and inadequate signage.
Last November, ten people lost their lives when a minibus drove off the road in northern Peru.