The old mastic may or may not be asbestos containing. There's no way to know unless you have it tested. I've seen both under old 9x9 tiles. Color is not a give away either. In any event, it is not a friable material unless you dry scrape it to create airborne dust. I've used Fiberlock products. What do you plan to put down in place of the tiles that were removed? Any mastic you put down to adhere a new floor will essentially encapsulate the old mastic.