Which African ethnic group believes that the gods are always watching and they will either bless or curse a person based on his or her behavior?

The Bantus.

Explanation:

The Bantus or the Bantu people are a group of indigenous African ethnic groups who are mostly found in the sub-Saharan regions of Africa. The most notable similarity among the Bantu people is the usage of the Bantu languages which are divided into about 440 to 680 distinct languages.The Bantus are traditional people and belief in supernatural elements. They belief in nature and also believes that the gods are always watching and they will either bless or curse a person based on his or her behavior.