Does at least one of the following apply to you?
1. You were engaged in a U.S. trade or business during the tax year.
2. You received U.S. source income for which your tax liability was not fully satisfied through withholding at source during the tax year.
Some examples of U.S. source income:
Income you receive for services performed in the United States
Rental income from properties located in the United States
Most income paid to you by U.S. domestic corporations, U.S. citizens or resident aliens, or entities formed under the laws of the United States or a state
Who Must File
You must file a return if you are a nonresident alien engaged or considered to be engaged in a trade or business in the United States during the year.
Even if you are not engaged in a trade or business in the United States, you must file a return if you have U.S. income on which the tax liability was not satisfied by the withholding of tax at the source.
You also must file an income tax return if you want to claim a refund of excess withholding or want to claim the benefit of any deductions or credits (for example, if you have income from rental property that you choose to treat as income connected to a trade or business).
Tax Treatment of Nonresident Alien
If you are a nonresident alien engaged in a trade or business in the United States, you must pay U.S. tax on the amount of your effectively connected income, after allowable deductions, at the same rates that apply to U.S. citizens and residents. If you are not engaged in a trade or business, the payment of U.S. source income that is fixed, determinable, annual, or periodical is taxed at a flat 30 percent (or lower treaty rate) and no deductions are allowed against such income. You may earn both effectively connected income and fixed determinable, annual, or periodical income in the same year and they will be taxed accordingly.