Moffett (44), who was said to have links to the loyalist terror group the Red Hand Commando, was gunned down by two men on the Shankill Road around 1pm yesterday.
The man, 40, was arrested last night and is being held at the PSNI's serious crime suite in Antrim.
Moffat was shot a number of times in the face by two masked gunmen in an assassination that has been blamed on renegade elements within the Ulster Volunteer Force (UVF) - a mainstream paramilitary group with historic ties to the RHCs.
It is understood the murder was linked to a personal dispute.
Police described the murder as "a cold-blooded, ruthless killing".