MI5 had raised the threat level for the region to "severe" about a year ago, following attacks on police officers and weeks ahead of celebrations marking the 25th anniversary of a peace deal that largely ended three decades of violence, Reuters reported.
The latest downgrade to the threat level is "testament to the tremendous efforts of the Police Service of Northern Ireland and MI5 to tackle Northern Ireland related terrorism," the British government's Northern Ireland Office said in a statement on Wednesday.
The decision to change the threat level is taken by MI5, independently of government ministers.
While the 1998 Good Friday Agreement largely ended sectarian violence in Northern Ireland, police officers can sometimes become targets for small splinter groups of mostly nationalist militants opposed to Britain's rule over the region.
The change to Northern Ireland's threat level brings it in line with the national threat level for the UK.