human activity vs human action

human activity and human action both are nouns.

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

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

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

Other synonyms of human activity include act, deed.

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