"I've thought about retirement, but not when the British are saying we want regime change," the 89-year-old president told Kyodo News in an interview in the Japanese city of Yokohama.
"I won't be changed by the British. My people will change me."
Mugabe has ruled uninterrupted since independence from Britain in 1980, despite a series of disputed and violent elections and a severe economic crash propelled by hyper-inflation.
He has been widely condemned for human rights abuses.
The president signed a new constitution into law last month, clearing the path to crucial elections later this year.
The charter introduces presidential term limits and strengthens parliament's powers, but could allow Mugabe to stay on for another decade if he wins elections.
Mugabe is visiting Japan to attend the three-day Tokyo International Conference for African Development ending tomorrow in Yokohama.
