Robin Garbutt, 44, was being questioned by detectives in connection with the death of his wife, Diana, sources said.
Mrs Garbutt, 40, was found dead in the upstairs living quarters of Melsonby Post Office, North Yorkshire, on 23 March.
Today, North Yorkshire Police said a man had been arrested in connection with the murder and suspected robbery of the post office.
A spokesman said: "The 44-year-old man, who is from the Richmondshire area, was taken into custody this morning, where he will be interviewed by detectives."
Detective Superintendent Lewis Raw, senior investigating officer, said: "The tragic death of Diana Garbutt three weeks ago has had a significant impact on people living in Melsonby and Richmondshire as a whole.
"It has also captured the concern and sympathy of the wider community due to the high level of media coverage of this case.
"I would again like to offer my sincere gratitude for the overwhelming support and understanding local people have given the police throughout this very complex investigation."