Who Must File a Tax Return?
In short, a person who is not a US citizen or resident must file a tax return that includes all US income.
If you are a student or a research scholar holding an F-1 or J-1 visa, you must file a form with the US tax agency, the Internal Revenue Service, even if you DO NOT have US income.
The rules and the processes of the Tax Assistance Program are different if you have US income than if you do not. If you only have income whose source is outside the US, you will follow the same rules as someone who has no US-source income.