Two RNLI lifeboats and a Coastguard helicopter were launched to search the sea around Castlerock and Downhill at about 18:40 BST on Saturday.
The search began following a call from a member of the public who became concerned after finding clothes on the beach.
RNLI beach lifeguards also searched the area on jet skis.
However, nothing was found and the search was ended shortly before 21:30 BST.
The Coastguard described the incident as a "false alarm with good intent".
The Coastguard and RNLI have stood down a major search operation off the North Coast following a "false alarm".