Potentially - it depends on how the antidepressant works. If the antidepressant actual is a drug all by itself and works by creating an inverse effect of the depressant, then yes, you are absolutely correct in that it is a stimulant. However, if the antidepressant by itself does nothing, except to destroy or otherwise neutralize the chemical functioning as the depressant, then no, it's not a stimulant and not really a drug, because it's not really doing anything to the nerve chemical receptors that a stimulant would - it's just preventing the depressant from doing it's job.

I believe that most antidepressants are, in fact, stimulants, but there probably are some exceptions that I don't know about.