If you do not see it in the list of Active-x controls, then the control is not registered in the computer. I assume that you have it installed on the machine. I don't have Matlab, and am not familiar with it, but if it is like all other Widows programs, it should register its controls when it is installed. Just in case it hasn't, if you know the exact name and directory path of the Active-x control,you can manually register it yourself from the DOS command line.
The syntax is c:\regsvr32 (full path to your active-x control) and enter. You will recieve a short message box telling you that you either succeded, or that it was already installed.
Try it, good luck
Dave