Yes, if you were present in the US during a calendar year, you are required to file tax paperwork in the following year. For example: if you were in the US in 2015, you must file tax paperwork in 2016 even if you did not work.
The US Internal Revenue Service is in charge of taxes. Please refer to their website for official forms and information.
GLACIER Tax Prep software is available free of charge to any international student or scholar with a UM/Ann Arbor uniqname and password.