No, a negative slope on a velocity vs time graph does not indicate that the object is not moving. A negative slope on a velocity vs time graph indicates that the object is moving in the opposite direction to the positive direction chosen for the graph. For example, if the positive direction is chosen to be to the right, then a negative slope indicates that the object is moving to the left. The magnitude of the slope indicates the speed of the object, and the sign of the slope indicates the direction of motion.