Yoga classes?

Hi maplesyrupchick, I invite you to post an advert in the section Classes of Antwerp classifieds, it may help.

Harmonie.

Some sport clubs offer them along with Pilates, dance, etc.

If not, go to any bio shop (use goggle to find the nearest to you) and grab one of the free magazines near the entrance. There you will find a long list of lessons/activities offered in your region.

Theres Yoga, and yogilates in the gym in the, mmm, there's this building in groen plats, which contains the hilton hotel. 's like a shopping center or something. Anyway, second floor is the gym, I think it's called "fit-in" or some other such name which has "fitness" in it.

You can try Health City (healthcity.be), they have gyms all over Antwerp, and whole Belgium too. And I've heard that they have also good yoga teachers.
Hope it helps