A geophysicist at the U.S. Geological Survey says the tremor happened about 80 miles off of Southampton at about 10:45 a.m. Tuesday.
The location also is 122 miles east/southeast of New York City.
He said it was a magnitude 3.9, which is considered very minor, especially since it happened in the Atlantic Ocean.
Southampton Town Police Sgt. Andrew Ficurilli says the police station shook for a few seconds.
He said "two or three" calls came in from town residents wondering what had happened.
Folks on Twitter and Facebook reported feeling the earth move for a few seconds in Melville, along the Manorville/Moriches border, Farmingville, Hicksville, Riverhead, Deer Park, Port Jefferson and Valley Stream.