The Czech Republic ace was awarded a free kick on the edge of the area after he was allegedly brought down by Inter defender Ivan Cordoba.
Italian veteran Alessandro Del Piero converted the free-kick home to give Juventus a 2-1 win over title contenders Inter.
“After the equaliser we tried to pour forward and get all three points, but Alessandro Del Piero scored a great goal. Having said that, Nedved is a diver," Mancini was quoted as saying by Football Italia on Sunday.
"He always throws himself on the ground and the referees fall for it. This is not up for debate, it was a simulation and he must earn about 10 free kicks per game like that," he added.
The game was tied at 1-1 after Inter after Walter Samuel's header cancelled out Zlatan Ibrahimovic's opener Juve.
Inter duo Luis Figo and Dejan Stankovic also voiced their frustration at the way Nedved was awarded the free kick.
"What has happened here is shameful. We should all go home - we should all go on holiday," Figo said.
"No way was that a free-kick, it wasn’t a bad foul. He just goes down whenever there’s a challenge and this episode cost us three points," Serbian midfielder Stankovic stated.