A 45-year-old man has been arrested over the Real IRA bomb attack on Palace Barracks in Holywood.
The bomb exploded outside the Army base which houses MI5's Northern Ireland headquarters on 12 April.
The explosion happened minutes after policing and justice powers were devolved from Westminster.
Police arrested the man in north Belfast on Monday moring. A number of previous arrests have been made over the attack but no-one has been charged.