Not sure where you are from, but usually if you are not a US citizen and are a non-US resident, you do not have to pay tax in the US.
Typically you would have to declare your trading income in your home country should you be defined as a resident there for tax purposes, ie reside there for more than 183 days a year for quite a few commonwealth countries - although that may not be sufficient â and depending on the country, other tests are likely to apply. chrs