The English noun floor, meaning floor, is a common noun, and usually must be accompanied by an article (either the indefinite article or the definite article). To say "on the floor" you must say on the floor, not on floor, which is clearly wrong.
The questioner may have confused the meaning of a synthetic adverb with that of a prepositional phrase acting as an adverb. For example:
onstage On the stage?
= on the stage?
downstairs Downstairs
= down the stairs
upstairs
= up the stairs Upstairs
underground
= under the ground