No, it's not legal- even if that anime is not licensed in the United States. The Berne Convention is a treaty that protects International Copyrights. japón and the US are both member States, party to this treaty. So when tu download and subir copies of something that is copyrighted in Japan, then tu are violating international law.
NOW, there is one thing to understand. Even though por the definition of the law, it is illegal, in practice it is hardly something that is ever enforced. Local companies that have licensed anime (eg Funimation) have taken action against US citizens (usually in the form of Cease and Desist orders), but I have yet to hear of a Japanese company taking action against a US citizen for downloading / uploading unlicensed anime. However, japón has become más and más proactive about this sort of thing lately.
And also, japón and license companies such as Funimation usually go after the fuente directly, and largely ignore us little people. Fansub groups and anime hosting sites are fair game, however.
So to sum up: Yes it is a violation of International Law (via the Berne Convention) to download and subir anime- however, it is highly unlikely for tu to get in trouble for merely torrenting anime- usually they go for bigger fish. However, tu still torrent at your own risk.