Go to "Windows" Menu
Choose "Show Mix"
In the mixer view, make sure you can see the left side of the mixer.Under the "Show Hide" Column find the "Mix Groups"
section.
If you click on your mix group (it may be number 1, or whatever
number of groups you created)
Clicking on it will change it's color from Color to White.
When its white, your group is "ungrouped"