Yes. Scratch 3.0, which uses HTML5, is supported on mobile devices. Nonetheless, the editor is not fully optimized for mobile yet, and many projects, especially those made in previous versions, are incompatible.
Previous Versions
Scratch 2.0 required the Adobe Flash Player to run or edit projects. It could be used on mobile devices that had Flash. There has also been a app called ScratchJr that can be used without Flash. However, it is very different from Scratch. One could still post in the forums and leave comments without Flash.
