FALSE RA'S CAUSING PLT TO DEVIATE FROM APCH COURSE.

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THE FO WAS TURNING ONTO A VISUAL APCH FOR RWY 28L AT SFO WHEN TCASII ALERTED US TO A TARGET AT 12 O'CLOCK; 50 FT ABOVE OUR ALT. WE RECEIVED AN RA AND DSNDED AND TURNED TO AVOID CONFLICT. I QUESTIONED APCH ABOUT OTHER TFC IN THE AREA; AND THEIR RADAR NOR OUR VISUAL CHKS SHOWED ANY TFC. RWY 28R WAS CLOSED AT THE TIME AND WE WERE ISSUED A VISUAL APCH TO RWY 28L -- NOT THE APCH. THE AIRPLANE SLIGHTLY CROSSED THE FINAL APCH COURSE DURING THIS EVENT AND 2 OTHER SIMILAR EVENTS INBOUND. AGAIN WE QUESTIONED THE TWR AND NO TFC WAS OBSERVED ON THEIR RADAR. A STRONG 20 KT WIND OUT OF THE S ALSO CONTRIBUTED TO THE SLIGHT OVERSHOOT; BUT THE MAIN CAUSE WAS OUR CONSTANT SEARCH AND RESPONSE TO RA'S WHICH I NOW BELIEVE TO HAVE BEEN FALSE TARGETS. UPON LNDG WE NOTIFIED MAINT AND I CALLED BAY APCH TO SE IF WE HAD CAUSED ANY PROBS. THE SUPVR ADVISED ME THAT THERE WAS NO PROB. THIS IS A VERY DIFFICULT DECISION AS HAD THERE BEEN RWY 28R TFC AND AN RA WHICH OUR COMPANY POLICY CALLS FOR IMMEDIATE ACTION A MORE SERIOUS SIT COULD HAVE OCCURRED IN THE FUTURE IF WE HAD CAUSED ANY PROBS. THE SUPVR ADVISED ME THAT THERE WAS NO PROB. THIS IS A VERY DIFFICULT DECISION AS HAD THEIR BEEN RWY 28R TFC AND AN RA WHICH OUR COMPANY POLICY CALLS FOR IMMEDIATE ACTION A MORE SERIOUS SIT COULD HAVE OCCURRED IN THE FUTURE IF I HAD TIME TO ANALYZE I WOULD DEFINITELY TURN L IF THE TARGET WAS AVOIDABLE IN THAT DIRECTION. THIS SIT IS VERY UNUSUAL AS I HAVE ONLY HAD FALSE TCASII RA'S ON ONE OTHER OCCASION. UNFORTUNATELY; TCASII DOESN'T ALWAYS WORK!