The office of Germany's first black MP was the target of an arson attack after death threats and shots fired against the building in previous years.
Karamba Diaby, an MP with the political centre-left Social Democratic Party (SPD), tweeted: "Happily, no one has been hurt."
"This act makes me angry," he said, adding that his offices would be out of service for some time.
Witnesses alerted by the flames late on Wednesday detained a man at the scene and a judge ordered him to be taken into custody.
According to Mr Diaby, a German of Senegalese origin, the person in question had already racially abused him.
"I'm horrified that a new, cowardly attack has been carried out against the constituency office of my Bundestag colleague," said Saskia Esken, co-president of the SPD.
Mr Diaby, 61, was born in Senegal but has had German nationality since 2001.
In 2020 he reported having received death threats from right-wing extremists after having found holes that appeared to have been made by a pellet gun in a window of his constituency office.
There is growing concern in Germany at a rise in incidents against deputies, from verbal abuse and assaults to death threats.
The political climate has become more polarised with the growing strength of the far right.
In June 2019 a neo-Nazi activist killed politician Walter Luebcke, in a crime that shocked the country and highlighted the growing threat of right-wing extremism.
A conservative politician, Mr Luebcke had defended the pro-migration policies of then-chancellor Angela Merkel.
In January, prosecutors charged five Germans with treason over a far-right plot to overthrow the government, which included plans to abduct the health minister.
And in a separate investigation, police said last December they had uncovered a plot to overthrow the government by a far-right group, which included a former deputy and an aristocrat.
