On its own, no it is not, but there are a range of antibiotics known as Sulphonomides that do contain this and they are known by trade names such as Septrin, so yes, sulphur is a component of antibiotics but not the only one.
I have to say that I would be very careful with these, as they are very strong and can cause a lot of allergic reactions and docs tend to prescribe other things in preference now, unless absolutely indicated.
I remember years ago being given Septrin by my doc for a severe chest infection. I took it for a week and by the end of the week was covered from head to toe in a rash and then had to take Piriton to help the rash. That was in the days before I knew any better and I have not taken it since, so be careful.