Mirren, 66, won an Oscar for her performance in "The Queen." Her other film credits include "Arthur," "State of Play," "National Treasure: Book of Secrets" and "Gosford Park."
The New York Daily News said she received 17.7 percent of the votes cast by 2,000 respondents to the survey. She beat out supermodels Elle Macpherson and Kelly Brook, actresses Jennifer Lopez and Kate Winslet and royal in-law Pippa Middleton for the title.
Middleton, who became famous after her sister Kate married Britain's Prince William in April, won the award for "Rear of the Year," the Daily News said.
"It's great to see the public celebrating bodies of all shapes and sizes, and proving that you really can look fabulous over 40 and 50," LA Fitness spokesman Tony Orme told the newspaper.