Police received a report that an injured man was discovered in Bath Terrace of Portrush shortly after 2.20 am.
They have not released any details about the victim’s age.
Detectives from the PSNI’s Major Investigation Team have appealed for anyone who was in the area on Sunday night or the early hours of Monday and witnessed anything to contact them.
The man who was arrested was detained on Monday evening.
Church Pass, Bath Terrace and Bath Street have reopened to motorists and there is now pedestrian access between Bath Street and Arcadia.
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