I found this on the floor and I don't know if this belong to the Prius or something else, does anyone recognize this piece?
I don't recognize it from being anything from a Prius. It appears to be some kind of control knob from a electronic device. I have to ask, have you recently purchased this car, used?
Yes I bought this car used and have kept this thing ever since. Glad to know I can finally throw this away !
It's a plastic cover for a screw. I'm with @WolfpackBill , I think it's a cover for one of the screws for the kick panel on the driver's side next to the dead pedal.
I agree. I believe it’s part number 90467-06193-C0. Toyota calls this a “CLIP” in the catalog, but it’s really a plastic cap nut that screws onto a threaded stud to retain a cowl side trim board. There is one on each side, as shown in figure 64-01 from the Electronic Parts Catalog, near the lower-left corner of the drawing.