Oscar was cautioned for diving in Wednesday's 3-0 win at Southampton as he tried to buy a penalty from Kelvin Davis, only for Martin Atkinson to produce a yellow card for the Brazilian.
While Mourinho agrees with that decision, he insists it was a one-off mistake from the 22-year-old, and is a firm believer that none of his players can be classed as a cheat.
Oscar's booking was not the first diving controversy at Chelsea this season.
Ramires was accused of going to ground easily to win a cheap penalty in stoppage time of November's 2-2 home draw with West Brom - which preserved Mourinho's unbeaten Premier League run at Stamford Bridge.
But the former Real Madrid boss sees no cause for concern among his players.
"It's impossible for him (Oscar) to get a reputation, unless somebody wants to be unfair and to clean the image of other people by using Oscar's situation in the last game," the Portuguese said.
"I want to make it clear. There are many divers in the world of football. There are many divers in some big clubs in the world of football.
"There are some divers in England. Not many, some. In Chelsea, no divers, no divers at all.
"Oscar made a mistake, which he tells me and I believe him, he was completely convinced the goalkeeper was coming to smash him.
"The goalkeeper didn't, he made his mistake, he was punished with a yellow card, he accepted the yellow card in a very calm way.
"His manager comes after in the press to say 'well done Mr Atkinson'. End of story. Here we don't have divers."
