The offices at Foyle Chambers in the Waterside area were evacuated on Monday morning and army bomb experts were tasked to the scene.
The alert has now ended and police have confirmed that a package contained a viable device which has been removed for further examination.
Police have said the device is similar to those found on Friday which were addressed to PSNI Chief Constable Matt Baggott and another senior serving police officer.
"Police would continue to ask members of the public to remain vigilant when opening their mail and anyone who notices anything suspicious should contact the police immediately," a spokesperson commented.
Justice Minister David Ford insisted that the justice system in Northern Ireland will continue to fully serve the community despite the attempted attacks.
"Yet again we see members of our community put at risk as a result of the actions of faceless individuals who represent no one and have absolutely nothing positive to offer," the Alliance leader said.
"They, and anyone who supports them in any way, are to be condemned in the strongest possible terms."
This latest attempt to attack those involved in the delivery of the justice system has highlighted the importance of securing a successful outcome to the Haass talks underway.
Justice Minister David Ford
SDLP Foyle MP Mark Durkan has condemned those responsible for the attack.
"Once again we have yet another example of the disruptive impact of the violent efforts of so-called dissident groups," Mr Durkan said.
"Those responsible for leaving this device have shown complete and utter contempt for the people of Derry. They are out to destroy, and don't care if they injure or kill anyone in the process.
"This callous and dangerous act flies in the face of the efforts made by so many people to improve life here."
He added: "Thankfully no-one has been injured but those graces are no thanks to those who were behind this attack."
DUP Deputy Mayor Alderman Gary Middleton also hit out at those behind the attack.
"It is very very worrying for the staff who are put at risk. But not only that, the postman as well. His life was put in danger," he said.
Sinn Féin Waterside Councillor Bridget Meehan said the device's discovery was "a very worrying development".
"(It) no doubt will have caused great concern to members of staff there and local postal staff," she said.
"This comes against a backdrop of alerts in the Top of the Hill area on Saturday and last week's incident at Charlotte Street.
"These incidents serve no purpose and those responsible need to come forward and explain to the people of Derry what the point of all this is."