power steering fluid in my brake master cylinder

Yes if you catch it in time, need to bleed all 4 corners if its been driven.

If you haven't driven it you could use a turkey baster or similar item and suck all the fluid out of the master cylinder. Then take a lint free cloth or paper towel and clean the rest out, then refill with the proper brake fluid (type is usually marked on the fill cap). If it has been driven then bleeding will be required after a refill. I would not wait long before changing the fluid.