One of the five wounded was hospitalized in serious condition, Bild.de reported.
Police said the shooting broke out during a meeting of apartment owners, the news website said. Police said the gunman got involved in an argument with the apartment owners, left the meeting and then opened fire when he returned, Bild.de said.
"The exact background, motives and the exact sequence of fact are still unclear," a police spokesman said.
Bild.de said police cordoned off a wide area around the restaurant after the shooting started. There had been about 20 people in the building and authorities brought in counselors and psychologists to deal with the traumatized witnesses.