TIU detectives supported by officers from the crime operations branch and the Tactical Support Group are conducting a number of searches in the Antrim Road and Duncairn Gardens area of the city.
Army Technical Officers also attended the scene after being tasked and an item was taken away for further examination.
A number of people have been evacuated from their homes as a a precaution while the security operation continues.
Two men, aged 36 and 37, were arrested under Section 41 of the Terrorism Act.
They have been taken to Musgrave Serious Crime Suite where they are currently helping police with their enquiries.
Detective Inspector Andy Workman of the TIU said: “Detectives are currently carrying out a number of searches in the Antrim Road / Duncairn Gardens area of north Belfast.