Is uniform circular motion in equilibrium?

(first answer) No.

For a system to be in equilibrium, there must be NO .

In uniform , we must have at least centripetal acceleration because the direction is constantly changing.

See the physics classroom for more information on circular motion: http://www.physicsclassroom.com/class/circles/Lesson-1/Acceleration

(second answer) The answer could be yes or no. It depends on which type of equilibrium you are referring to.

Uniform Circular Motion (UCM) means that the angular acceleration is zero, which means the object has a constant angular velocity. (note: it could still be at rest, the angular velocity would be a constant zero.)

An object in UCM is not in translational equilibrium. Translational equilibrium means the net force equals zero. According to Newton's 2nd Law, this means that the linear acceleration is equal to zero. which means the object has a constant linear velocity (again, could be zero). An object moving in a circle must have an inward, centripetal acceleration, which means this linear acceleration will not be zero, hence not in translational equilibrium.

An object in UCM is in rotational equilibrium. Rotational equilibrium means the net is equal to zero which means the angular acceleration is equal to zero, which is the definition of UCM.

You should check out my video: The Differences between Angular, Tangential and Centripetal Accelerations. It will probably help.