Sihanouk made the announcement in a letter to Prime Minister Hun Sen that was dated Tuesday and posted on his official Web site Wednesday.
The 83-year-old former monarch and his wife, Monineath, are currently in Pyongyang where they maintain a residence built for them by the late North Korean dictator Kim Il Sung.
Sihanouk said his son, the current king, Norodom Sihamoni, will visit North Korea and accompany him and his wife back home in May.
Sihanouk left Cambodia in August last year for a routine health checkup in Beijing, China's capital.
In a letter to Sihanouk last Friday, Hun Sen lamented that the former king has been away for "extremely too long" and pleaded with him to come back before Cambodian New Year in mid-April.
Hun Sen said people "have been constantly thinking" about the royal couple and asked when they will return to stay with them.
Sihanouk replied by saying threats and media criticism aimed at him have kept him away but failed to be specific.
In his letter, he said he reversed his early decision after carefully considering Hun Sen's request, reports the AP.