They're usually made of an off metal for starters but I'd take it to a coin dealer that is familiar with ancient coins to get their opinion. I assume it doesn't say "copy" on it anywhere?
It does? I think it's much more likely to be found in Europe but immigrants to this country brought all kinds of different coins with them over the centuries. Not to mention that they can be fresh drops from somebodies collection or "pocket" good luck charm.