be anxious and preoccupied; agitated; be on tenterhooks; be distracted; be all in a twitter; feel ill at ease; feel restless; fidgety; have no peace of mind; in a state of discomposure; out of sorts; miles away; wandering in thought
I don't know what is on his mind; he always looks restless.
不知他有什么事， 老是心神不定的样子。