Paul Rusesabagina, a Hutu, became well known after Hotel Rwanda depicted his efforts to save hundreds of Tutsis at his hotel during the 1994 genocide.
He later launched an opposition party, which had an armed wing based in the Democratic Republic of Congo.
About 800,000 Tutsis and moderate Hutus were killed in the genocide.
They were killed by Hutu extremists who were forced from power by President Paul Kagame and his Tutsi-dominated Rwandan Patriotic Front (RPF).
Mr Rusesabagina, 66, has received several human rights awards for his life-saving efforts, including the US Presidential Medal of Freedom in 2005.
He was paraded by the authorities at a press conference in the capital, Kigali, after he was arrested under an international warrant.
He had been living in exile. The authorities did not say where he was arrested or give any further details about the accusations he faces.