A district court in Siegen, near Cologne, confirmed the 36-year-old, who has made five appearances for Germany and was part of the 2014 World Cup squad, was banned after being caught speeding in a 100km/h zone in August.
After being caught by a speed camera, Weidenfeller initially contested the ban, which would have meant a court appearance, but opted to accept the decision and has also been fined 600 euros ($639).
Having lost his place in goal for Dortmund at the start of the season, Weidenfeller was reinstated by Borussia coach Thomas Tuchel last month after first-choice Roman Burki suffered a hand injury.