OR: Can an object with constant acceleration reverse its direction?
Yes. When a moving body is acted by a constant opposing force, its velocity decreases and it ultimately comes to stop. If the constant force is still acting, the body will start to accelerate but in opposite direction, which means the direction of velocity also reverses.
[Read: Motion in a Straight Line]
An example of such a case is projectile motion. When a body is thrown vertically upward, at highest point, its acceleration becomes equal to the constant acceleration due to gravity $(g)$. And, the body changes its direction from upward to downward. So, the direction of velocity of an object can change keeping the acceleration constant.
[Read: Motion Under Gravity]
Also, when an object is moving in a circle [Circular Motion], its acceleration is constant and towards the centre of the circle but the direction of velocity is changing continuosly. After the half period of revolution, the velocity of the object reverses its direction.