IN OUR SYSTEMATIC SEARCH FOR SERENDIPITOUS SOURCES (SERENDIPS) IN THE NUSTAR DATA WE HAVE FOUND A VERY BRIGHT (7.5 MCRAB IN THE 2-10 KEV BAND) SERENDIP (J0923_S1) NEAR THE EDGE OF ONE OF THE NUSTAR FIELDS OF VIEW. THE SOURCE HAS BEEN PREVIOUSLY DETECTED IN THE SOFT X-RAY BAND BUT ITS NATURE IS UNKNOWN. BASED ON ITS X-RAY SPECTRUM ITS OPTICAL COUNTERPART AND ITS LONG-TERM VARIABILITY (AS SEEN BY MAXI) IT MUST BE GALACTIC AND WHILE SOME OF ITS PROPERTIES ARE SUGGESTIVE OF A MAGNETIC CATACLYSMIC VARIABLE OTHER PROPERTIES CAUSE PROBLEMS WITH THIS INTERPRETATION. ONE INTERESTING POSSIBILITY IS THAT IT MAY BE AN ACCRETING BLACK HOLE WITH A HIGH TEMPERATURE DISK. WE PROPOSE NUSTAR AND XMM-NEWTON OBSERVATIONS TO DETERMINE THE NATURE OF J0923_S1.