Ursula Haverbeck has often denied the mass murder of millions of Jews by the Nazis, which constitutes incitement of racial hatred under German law.
And although she has been convicted on several occasions, she has not served any jail time, as the cases are all still under appeal.
During a public event at the end of January, Haverbeck repeated her claims, saying it was "not true" that there were gas chambers at the Auschwitz death camp.
She also disputed the fact that 1.1 million people were killed at the concentration camp in Nazi-occupied Poland.
During her trial, Haverbeck argued that she was only quoting from a book that she was presenting at the event.
She also filed an immediate appeal against Monday's ruling.
Dubbed the "Nazi grandma" by German media, Haverbeck is a notorious extremist who was once chairwoman of a far-right training centre shut down in 2008 for spreading Nazi propaganda.
She had also appeared on television to declare that "the Holocaust is the biggest and most sustainable lie in history".
A court spokeswoman said that Haverbeck would only be imprisoned if an appeal fails and if she is deemed fit to serve time in prison.