Yes. Probably it is some Armillaria, but maybe other species. Fungi likes dead wood (and dead roots) as nutrient to grow. Fungi cannot produce own food (evolutionary, they are more related to animals than vegetables), so they need to find nutrients.
You should remove them, and in a few years they should reduce, until they will find no more root. Next time, when you remove a tree, try to remove as much as possible his roots (especially root near surface).
If you are lucky, the fungi are on another species, which like just the chips (produced by cutting the tree). In this case chips will disappear a lot quicker.