Methionine is a nonpolar amino acid because it has a nonpolar side-chain.
We usually write the general structure of an amino acid as
The molecule therefore exists as a "zwitterion",
Thus, it usually has a charge at one end or the other and is a polar species.
However, the term polar amino acid usually refers to the side-chains that will impart a more polar character to the amino acid.
Side chains with functional groups such as acids, amides, alcohols, and amines do impart a more polar character to an amino acid. They form polar amino acids.
The structure of methionine is
We see that the
Thus, methionine is a nonpolar amino acid.