I wonder if "Keep looking back" can describe the act of looking back repeatedly at an interval of a few seconds.
For example, you are walking along the sidewalk and a man is walking in the same direction as you are. And while he is walking, he looks back at you for a second and keeps looking forward and this happens again and again like at an interval of several seconds.
This is not him looking back continuously but it is repeated.
In this case, can we say "He keeps looking back (at us) while walking. He is suspicious."?