Officers arrived at the scene at 3.49am on Sunday (May 16) and said the man was reportedly making threats outside the station.
Brighton railway station was temporarily closed to the public and a cordon was set up as a safety precaution while officers carried out an extensive area search.
On Monday (May 17) police said: “A 27-year-old man was swiftly detained and has been taken to custody for questioning.
“He was not in possession of an explosive device.”
An additional sweep of the area was carried out by armed officers.
Superintendent Justin Burtenshaw said: “This is being treated as an isolated incident and there is not thought to be any threat to public at this time.
“The cordon has now been lifted and train services have resumed from Brighton Railway Station.
“Officers remain at the scene working with British Transport Police to carry out further enquiries.
“We are thankful to the public for their patience and understanding while we carried out our work.”