Seedorf, who took over at Milan in January, has overseen a slump in form as the Serie A giants have lost five of their last six matches in all competitions.
Fan protests preceded Sunday's 4-2 home loss to Parma as ex-Milan forward Antonio Cassano bagged a double for the visitors.
Milan were also dumped out of the UEFA Champions League by Atletico Madrid last week and the club's supporters have lost patience.
Seedorf and a number of key players met with Ultras leaders after Sunday's defeat in a bid to calm tensions and Berlusconi has now given former Milan midfielder Seedorf a vote of confidence.
Berlusconi told SkySport24: "Seedorf is not up for debate.
"He will still be the Milan coach next year. Milan are a badly built team."
Milan sit 11th in the Serie A table, a whopping 40 points behind leaders Juventus and 12 points behind city rivals Inter - who occupy fifth spot.
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