Police did not give a figure but Folha de Sao Paulo newspaper said on its website that some 20 buses were torched in a garage where unused vehicles were stored on Tuesday (Wednesday AEST).
Another three buses were set ablaze in other parts of the city.
Police did not confirm whether the fires were linked to Brazil's 7-1 defeat to Germany in the semi-final, which knocked the national team out of the World Cup.
"This is under investigation," a state police spokesman told AFP.
Looters ransacked an electronics store in the east of the city.
Buses are often burned by robbers or as a form of protest in Brazil.
View of a burnt out bus by soccer supporters after the FIFA World Cup 2014 semi final match between Brazil and Germany, at Yervant Kissajikian Avenue, in Sao Paulo, Brazil, 08 July 2014. (AAP)
