I am balancing an aluminium roller using Dynamic balancing machine for G6.3 grade. I find the roller after balancing & assembling on the machine, will rotate. Actually if the roller is balanced it should not rotate in the reverse direction after it comes to rest. Whether the dynamic balancing machine is not giving proper results or is there any other unseen problems.

I'm unclear on the specifics of what you are doing, but as a general reply I can make some comments. When you dynamically balance your roller it should be moving, and your balancing about a centroid that's the average of the roller's mass distribution. If we assume you balanced the roller dynamically as best as you could, and the roller is free of other influences, then what you see is gravity is acting on an asymmetrical mass distribution about the roller's axis. That is, your roller is lopsided and the dynamic center of gravity is not the same as the static center of gravity. You can test this and get some feel for the situation by marking sections on the roller's end, numbering them, and rotating each to the top, releasing the roller, then seeing which way the roller turns. All rollers are lopsided to some degree. If this matters or not depends on the application. If you even see this depends on the asymmetry and the roller's friction.