Kean celebrated by holding his arms outstretched to the home supporters at Sardegna Arena after scoring in Juve's 2-0 win last month.
The 19-year-old later posted an image of the celebration on his Instagram account with the caption: "The best way to respond to racism."
Juve defender Leonardo Bonucci was widely criticised after he suggested the Italy striker had provoked supporters, while Cagliari's chairman Tommaso Giulini denied hearing racist chants.
The Italian Football Federation (FIGC) announced it was investigating the matter but Lega Serie A announced the case has been closed on Wednesday (AEST).
This announcement was condemned by Kick It Out, a UK-based anti-discrimination campaign group, which hit out at the FIGC over the matter.
"Embarrassing. Pathetic. Disgraceful," Kick It Out posted on Twitter in response to the news.
"Racism will never be kicked out of football while decisions like this continue to take place — @FIGC should hang their heads in shame."
Kean, one of Italy's brightest young players, was ordered to pay a €2000 ($3217) fine for an act of simulation during the Cagliari contest.