Question

If there is only one force acting on a body, can it be at rest ?

Answer 1

yes, gravity creating a normal force on an object on a flat surface

Answer 2

no, never if only one force is acting on an object it can't be in rest. if it seems that on a rest body there is only force acting, this is just misunderstanding there will be surely an another force that is nutrilising that force. in case of gravity creating a normal force on an object on a flat surface there is an another force(normal force perpendicular to surface) is acting on opposite direction.

Answer 3

Both make pretty good points.