Around 90 rocket canisters were recovered in the waters off Claveria, in the northern Luzon province of Cagayan.
Fishermen found 24 wooden crates containing the warheads, Philippine National Police chief General Debold Sinas said.
The canisters have US warhead markings and could have been brought to the country for the annual Balikatan exercises.
An inspection by personnel of the Explosives Ordnance Division/K9 Group showed the canisters were negative for any explosive or hazardous materials.
Sinas said unknown foreign vessels could have dropped the crates which could have been at sea for a long time. The locks and hinges were rusty and the wood is in a state of decay.
Sinas said, “We assure local leaders and the people of Claveria, Cagayan that there is no cause for alarm over the discovery of these items.”
The PNP added it would coordinate with the US government to determine if military exercises were conducted in Claveria.