In the United States, the term adjusted gross income has the smell of US Federal Tax Form 1040, and accordingly, yes; which is both a shame and a sham as the younger you are, the less likely it is you will ever, ever — which is to say never — see any of this withheld Social Security.
This article originated as an answer to a question on Quora: https://www.quora.com/Is-Social-Security-included-in-adjusted-gross-income.