Mancini backed Hart following criticism of his performance in England's 4-2 friendly loss to a Zlatan Ibrahimovic-inspired Sweden in midweek.
Mancini said: "The keeper sometimes can make a mistake, this is normal.
"If a keeper makes a mistake, you concede a goal and you lose. If the striker doesn't score a goal the game can finish 0-0.
"This is a keeper's life but Joe is a top keeper.
"Ibrahimovic can score against every keeper. Ibrahimovic for me is one of the top five strikers in the world."