Sure there is. In Marktplatz (market square), open from Nov 27 to Dec 20.
However, I hope you have planned time to see the one in Erfurt, too?
Yes, We are going to Eisenach from Frankfurt. Next day Erfurt and then Weimar and back to Frankfurt via Wurzberg and Mittenberg and maybe Bamberg if we have time. Short trip but we love the Xmas markets! Is Weimar as good as Erfurt? Do you also comment on Bamberg, Wurzberg, and Mittenberg? Our last trip was to Dresden, Leipzig, and several towns in the Erzgebirge - fantastic, all of them!