Answer
The locus is the perpendicular bisector of line segment AB.
Work Step by Step
Recall, a locus is equidistant from the points no matter where you are. Therefore, first construct the original points. Then, draw a line (which is red in the diagram) that is equidistant away from the points at all points. There is a theorem that states that this will be the perpendicular bisector of line segment AB.