No. Some exercised stock options are considered compensation and subject to FICA (social security and medicare tax).
See page 7 at http://www.taxwarriors.com/hs-fs/hub/127975/file-17012949-pdf/docs/rl31458.pdf
No, FICA & Medicare is your social security withholding - not federal income tax withholding.
To clarify: Qualified stock options are not subject to FICA where Non-Qualified options are. Presumably the options you exercised were Non-Qualified.
Tom Young