A US nonresident alien has special rules because your not a citizen. But, generally a nonresident alien is not required to pay social security on income in the US if it is related to a foreign nonresident students studies. But if it's a general part time job or something then you'd have to pay like everyone else.

Also, you are not taxed on your worldwide income because you'd only be paying tax on your US income. Thus, you'd only be taxed on income earned in the united states.

conclusion: options are not taxable if ur an employee because they'd probably be qualified. Stock grants probably would be taxable since ur getting gross income in the form of stock or equity.