The winner was announced three weeks before Real Madrid and Liverpool will face off on May 26 in Kiev, Ukraine.
On the website the words “Season 2017/18” with Liverpool’s crest were seen. Below that the word “Winner” was written under Liverpool.
Although the error was quickly fixed, Twitter users took pictures of the website and posted it online.
The final match will determine the best team in Europe.
Earlier, another gaffe took place when Roma had advertised tickets for fans to go to their home leg against Liverpool despite the two club's names having not yet been pulled out in the drawing.
Liverpool made it to the final with a 7-6 aggregate semi-final win over Roma.