Over the past year, dissident republicans have significantly increased their activity.
In November, they were behind a proxy car bomb intended for Belfast city centre.
The 130lb device, which was intended for the underground car park of a major shopping precinct, partially exploded while army bomb disposal experts attempted to disarm it.
Police said had the device fully exploded it would have been "catastrophic" for the city and Northern Ireland.
Later, a suspect bomber was engulfed in flames after a device exploded as he was about to plant it in a city centre store.
And during one of the busiest nights of the festive period another bomb partially exploded in the Cathedral Quarter area of the city causing widespread disruption.
In response police were forced to up security around the city and there was a return of Troubles-era security and vehicle checkpoints put in place on routes into Belfast and at entrances to shopping centre car parks.
Chief Constable Matt Baggott said dissidents were targeting the economy in a change of tactics and commended shoppers for supporting the city's trade.
However, he claimed international investment was being lost because of the attacks.
Security costs were defined as those unique costs incurred by the PSNI, over and above normal policing costs, as a direct result of the specific security situation in Northern Ireland now or in the past.
Meanwhile, during the past year, Loyalists have taken to the streets to protest at Belfast council's change in its flag flying protocol at city hall with a number of the demonstrations erupting into violence.
And contentious Orange Order parades have increased the security burden on the PSNI.
Loyalists are continuing to protest over a Parades Commission ruling which prevented three lodges from marching past the Ardoyne shops in north Belfast on the Twelfth last year.
Each night they hold a protest at police lines over the decision and a protest camp has been established at Twaddell Avenue.
Last December during one such protest, dissident republicans used military grade weapons to target police in the area.
At the time police branded the attack as "madness".
The number of public order units deployed for the ongoing nightly protests at Twaddell/Woodvale has also reduced over recent months, and therefore the cost of policing each event has steadily fallen.
Justice Minister David Ford said the security bill was 32% - or just over £260m - of the PSNI's £790m annual budget spent on such incidents.
Mr Ford said: "This includes the costs of policing the terrorist threat and also the costs of policing public disorder and parading."
The cost of policing loyal order parades and protests alone during the last six months was just over £6m the Justice Department said.
Additional costs included police overtime use of PSNI helicopters, catering and vehicle fuel.
Earlier this month, UTV exclusively revealed that the police overtime bill cost £72m in 2013.
That was £20m more than that spent the previous year, due to a combination of the terrorist threat, civil disorder and the G8 summit attended by world leaders in Co Fermanagh.
Mr Ford added: "In recent months there has been a reduction in the number of flag protests and the number of those attending.
"It is hoped that these costs can be further scaled back in the weeks and months ahead."
The Police Federation, which represents officers on the front line, said overtime would be better spent on recruiting more officers.
The organisation said the force needed 1,000 more officers to cope with the security situation.