Let n be any terminal.
Consider the following, presumably correct, representation of the kleene star over n:
N → n N | ε
(where ε is the empty terminal.)
Wikipedia says:
Every grammar in Chomsky normal form is context-free, and conversely, every context-free grammar can be transformed into an equivalent one which is in Chomsky normal form.
I cannot see how the above grammar could be transformed to CNF.
Fortunately, this can be written in CNF. Here is one such grammar:
S → ε | n | NA
N → n
A → n | NA
Therefore, the language is context-free.
Hope this helps!