After a first half with little goalmouth action, Natalio had a great chance to put Numancia in front but missed the target.
Neither side was able to make the breakthrough but there were eight yellow cards at the Estadio Nuevo Los Pajaritos.
A point sees Castilla climb up a place to 19th. They are still in the bottom four but now just two shy of safety. Numancia, meanwhile, stay 14th and are four points above the drop zone.