It is flowering!! Those are its blossoms!
They are attracting insects that like the nectar, which are usually the ones that are beneficial to have in your garden.
People generally don't let their herb plants blossom, because the quality and productivity go down after that. Time to harvest some mint. Clip off stems down towards the base, cutting just above a leaf node (that would be the place where you see a pair of baby leaves just coming out from the stem).
But yes, it is still edible.