human action vs human activity

human action and human activity both are nouns.

Word	Noun	Adjective	Verb	Adverb
human action	Yes	No	No	No
human activity	Yes	No	No	No

As nouns, human action and human activity are synonyms defined as:

human action and human activity: something that people do or cause to happen

Other synonyms of human action include act, deed.

human action (noun)	human activity (noun)
something that people do or cause to happen	something that people do or cause to happen