Is this table in 3NF?
No it is not.

Consider this data

id | name | city        | state      | country
----------------------------------------------
 1 | john | Los Angeles | California | USA
 2 | mary | San Antonio | Texas      | USA
 3 | joe  | Los Angeles | California | USA


It is clear that (city,state,country) is a candidate key for another table.  Then, you would quickly realise that the cities belong to the same (state,country) combinations.  Eventually, you end up with

Person
------
id
name
city_id

City
--------
city_id
name
state_id

State
--------
state_id
name
country_id

Country
----------
country_id
name