No, but it is taxable. Either as a legal Tender, it is something that will not happen in the near time, or it may not happen at all.
you can buy and use bitcoin in USA, and some of your trading deals are under tax
you can real all details from here --> https://www.irs.gov/individuals/international-taxpayers/frequently-asked-questions-on-virtual-currency-transactions RS issued Notice 2014-21, 2014-16 I.R.B. 938