The man was held on Wednesday morning under section 41 of the Terrorism Act 2000.
He was taken to Musgrave police station in Belfast.
Police also said a house in Derry was being searched during this morning's operation.
The 29-year-old journalist was shot in April 2019 while covering a riot in a Creggan estate, Londonderry. The New IRA said it carried out the killing.
Police Service Northern Ireland said in a statement on Wednesday: "Detectives from the Police Service of Northern Ireland's Major Investigation Team, investigating the murder of journalist Lyra McKee, have arrested a 27-year-old man in Derry/Londonderry this morning under Section 41 of the Terrorism Act 2000.
"He has been taken to Musgrave police station in Belfast where he is currently being questioned.
"A search of a house in Derry/Londonderry has also been conducted."
In February a 52-year-old man was charged with her murder and another man has been charged with offences relating to the rioting that preceded it.
In June, detectives recovered the gun that killed the journalist, who was renowned for her investigative work on the simmering tensions between dissident groups in Northern Ireland.
She was standing near a police vehicle when she was hit by a bullet that a masked gunman fired towards officers.
The Belfast writer was living in Londonderry at the time with her partner, Sara Canning.
The gay rights activist was an articulate advocate of a new and more tolerant Northern Ireland and part of the generation which reached adulthood during peace time.
She wrote for publications including Private Eye and Buzzfeed.
Her funeral was attended by then prime minister Theresa May, Irish Taoiseach Leo Varadkar and Irish President Michael D Higgins at St Anne's Cathedral in Belfast.