Kidman emerged from the luxurious harborside mansion she once shared with former husband Tom Cruise to greet about 20 reporters and photographers waiting outside, who brought flowers and sang "Happy Birthday" to the actress over the intercom.
Asked how she planned to spend her birthday, Kidman replied: "Not much, dinner at home with mum…boring."
Wearing a black coat against the southern hemisphere winter chill, Kidman said she was "embarrassed" by all the attention.
Later, the actress sent bottles of water and a case of beer out to the media pack with an attached note saying: "Enjoy! Nicole and Keith," the Australian Associated Press reported.
Kidman and Urban, 38, arrived in Australia on Monday amid widespread rumors they were set to wed, the AP reports.
There are several versions of the recent assassination of the most prominent Iranian nuclear scientist and high-ranking officer of the Islamic Revolutionary Guard Corps, Mohsen Fakhrizadeh