What could cause painless involuntary forehead tightening / twitching?

Facial nerve. facial nerve supplies the forehead muscles and anything that makes the facial nerve get active will cause this, idiopathic hemifacial spasm is the most common cause of this, sometimes it is from an actual compression of the facial nerve or due to its inflammation, consider neurological consultation for this issue as you need an MRI brain to r/o a mass and inflammation.