...
Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
RaycastHit mouseHit;
if (Physics.Raycast(ray, out mouseHit)) {
   GameObject hitObject = mouseHit.transform.gameObject;      
   if (hitObject.layer == LayerMask.NameToLayer("Ground")) {  
      _targetPos = mouseHit.point;
      _curSpeed = moveSpeed;
   }
}
...
