"We are very happy to be back in Australia," they said in a joint statement carried by Australian Associated Press. "We have come home to celebrate our wedding with our family and friends."
Australian media have widely speculated that Kidman, who will be 39 on Tuesday, and Urban, 38, will wed June 25 at a Catholic church in a northern Sydney suburb close to where Kidman, who was born in Hawaii, attended high school.
The Oscar-winning actress was photographed leaving a private jet as she arrived in Sydney early Monday.
Kidman told People magazine last month that she and Urban were planning to marry. "He's actually my fiance," she told the magazine after hosting a gala event in New York. "I wouldn't be bringing my boyfriend."
Urban's publicist, Paul Freundlich, later confirmed the couple were "happily engaged."
Kidman won an Oscar for 2002's "The Hours." Urban won a Grammy in 2006 for best male country vocal performance for "You'll Think of Me."
Urban and Kidman were first seen together last year.
Kidman and Tom Cruise divorced in 2001 after 10 years of marriage. The couple have two children, Isabelle and Connor.
Katie Holmes, who is engaged to Cruise, gave birth to the couple's first child, a daughter, Suri, in April.