Question

When a body is under certain stress, is it in equilibrium? How

Answer 1

Yes the body remains is in equilibrium unless their is no external force or torque.

Going by the definition of stress, " it is the restoring force that bring the body to its initial state or normal condition."It is concerned with the volumetric/linear/angular deformation.

So we can say that Stress has no effect on the external net force and net torque acting on the body and hence it remain in equilibrium.