For the 1.3-acre White Rock Island, a bid of 415,000 pounds had been made by the singer, a 22-mile boat ride from the Los Angeles shoreline, according to friends, reported Daily Star.
Williams fell in love with White Rock while UFO hunting more than a year ago with his wife Ayda Field, 33, who is expecting their first child.
"It's a dream location for him and means he, Ayda and the baby won't have to check into any local hotels where he's always recognised," said a friend.
Williams, who attended a UFO convention in Nevada, claims to have seen three flying saucers.
"He's in negotiations and he's thrilled at the prospect of buying White Rock. Ayda's hooked on his UFO kick," said a source close to the singer.