He said he would announce the election sooner rather than later, but gave no certain date for polling, the New Zealand Herald reported.
Key told his weekly post-Cabinet press conference that leaving the country to attend the meeting in Brisbane would be a "complicating factor" for an election campaign, the Herald reported.
The summit will be held in Brisbane, the capital of Queensland, Nov. 15-16.
"I don't know exactly when it [an election] will be,'' he said. "I know a few dates that might work, but I don't have an exact date.''
Campaigning would run four to six weeks and an election announced just before Nov. 15 means polling would be around Christmas, a poor time for an election day, the Herald reported.
The latest date for New Zealand to hold an election is mid-January, but conventional wisdom suggests that also is a terrible time to go to the polls.
Key has invited world leaders to visit New Zealand around the time of the summit.
However, the presence of foreign leaders in New Zealand before an election could be seen as an attempt to influence the contest, as well as diverting Key from important electioneering time, the Herald reported.
A visit by U.S. President Barack Obama would come soon after the announcement in November that the two countries have resumed military contacts after a hiatus of nearly 30 years.
The break was brought about by New Zealand's ban since the 1980s on nuclear-powered and nuclear-armed vessels visiting New Zealand ports.
The United States then issued a policy restricting visits by New Zealand warships to American ports, the U.S. Defense Department's American Forces Press Service reported.
Obama and Key last met when they got together for a game of golf during separate holidays in Hawaii in early January, Radio New Zealand reported.
A statement by the U.S. Consulate General in Auckland, New Zealand, said the leaders have long discussed their shared interest in the sport and have developed a close partnership including a commitment to enhancing regional security, Radio NZ reported.
Military relations started to thaw last year when then-Defense Secretary Leon Panetta visited New Zealand, AFPS reported.
A later meeting in the Pentagon between U.S. Defense Secretary Chuck Hagel and his New Zealand counterpart, Jonathan Coleman, in November opened the way for the first visit by a New Zealand naval vessel to a U.S. port in more than three decades.
The New Zealand navy will dock at Pearl Harbor, Hawaii, during the Rim of the Pacific -- RIMPAC -- military exercises in June and July.