If you or your parents come under OCI category, then you become ineligible to register for JEE Advanced as foreign national. Quoting the exact lines from the official website, "1. Who can apply as foreign nationals?

Candidates who are NOT citizens of India (by birth or naturalized), do not belong to OCI/PIO category, and whose parents are not citizens of India and do not come under OCI/PIO category at the time of registering for JEE (Advanced) 2019 are treated as foreign nationals. Seats allotted to foreign nationals are supernumerary with a cap of 10% of total number of seats in every course."

Link: https://jeeadv.ac.in/Foreign-Candidates.html