By mistake I put a silver mayim acharonim dish on the table on shabbos not realizing that it contained a coin that was put there before shabbos. Did that make the dish a boses and did that mean one could not move the dish off the table till after shabbos?
An object does not become a bosis unless the muktza item was placed on it with the intention of the muktza item remaining on the object for the beginning of Shabbos (an exception to this rule is when the object normally supports the muktza item, e.g. a wallet containing money). Accordingly, the dish did not become a bosis, one would be allowed to hold the dish and shake off the coin, and then move the dish.
All the best
Shulchan Aruch O:C 309:4, and Mishna Berura 309:14 and 309:18