A body is kept on a table. The object is pushed downwards with a force equal to its weight. But the table exerts an equal and opposite force on the object, hence keeping it at rest.
The weight of the object exerts a force on the table. The table in return exerts a reaction force which is equal to the magnitude of the weight and opposite in direction (Newton's third law). Thus, the net force on the object is zero as two equal forces in opposite directions are acting on it and hence the object remains at rest.