Mean ones to keep identity withheld? (4)
I believe the answer is:
anon
'identity withheld?' is the definition.
(anonymous)
'mean ones to keep' is the wordplay.
'to keep' says the answer is hidden in the clue.
'ANON' is hidden within 'mean ones'.
(Other definitions for anon that I've seen before include "Nameless - presently" , "Having no known name" , "prolific author" , "Mystery writer" , "Presently - unattributed" .)