Asked if she felt the Oscars are "behind the times" for failing to nominate a single black actor for the second year in a row, Mirren said, "It just so happened it went that way."
In an interview with UK's channel 4 News, Mirren, 70, accepted that while "Idris Elba absolutely would have been nominated for an Oscar", she felt that not many people saw or wanted to see "a film about child soldiers."
Elba failed to make the cut in the best actors' nominees list despite a powerful performance in "Beasts of No Nation".
The diversity issue became huge this year with a number of Hollywood celebrities criticising the all white acting nominations category.
Stars like Will Smith, wife Jada Pinkett Smith and director Spike Lee have decided to boycot this year's award.
Academy announced some major changes to make the nominations process more inclusive following the uproar over lack of diversity.