He was one of three men arrested in Belfast and Lurgan on Sunday by police investigating dissident republican terrorist activity.
Duffy, 47 and from Forest Glade in Lurgan, appeared before Belfast Magistrates' Court on Tuesday - where he also faced further charges relating to IRA membership, firearms and explosives.
His two co-accused - Henry Fitzsimons, 46 and with no fixed address, and Alex McCrory, 52 and from Sliabh Dubh View in west Belfast - are both charged with attempted murder of police.
The charges relate to an incident in the Crumlin Road area of north Belfast earlier this month when shots were fired at PSNI vehicles.
Officers were travelling to the scene of a loyalist protest at the time.
Fitzsimons and McCrory are both also facing charges relating to weapons and IRA membership.
The defendants waved and smiled at a group of supporters inside the court and did not stand when asked by the court nor did they answer to the charges.
They have been remanded in custody until 14 January when they will appear before videolink.
Two people were arrested amid scuffles outside the court on Tuesday.
The 32-year-old and 33-year-old have now been charged with assault on police, disorderly behaviour and resisting police to appear at Belfast Magistrates Court on 13 January.