Actively working (2,4)
I believe the answer is:
on duty
'actively working' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for on duty that I've seen before include "Working at a particular time" , "As working policemen are" , "What working nurses are" , "Engaged in one's regular work" , "(Of soldier) working" .)