In addition, state Home Secretary Herbert Reul said police found bomb-making materials in the possession of the teenager, according to the dpa news agency.
The student is suspected of plotting an attack on the Don-Bosco-Gymnasium, the school he currently attends, or another local school he previously attended, the Realschule am Schloss Borbeck, police said.
Police told broadcaster ZDF they had evidence of a crime in which “weapons played a part”, but gave no further details.
Thursday, the suspect was in custody.
Both schools were closed on Thursday due to police operations. A statement on the Don-Bosco-Gymnasium website on Thursday morning said they had “received indications that a crime was planned at the school”.
Thomas Kutschaty, the state parliamentary leader of the center-left SPD, tweeted on Thursday that reports of the alleged plot “shocked me deeply”. He praised the “high level of civil courage and courageous police intervention” which ensured the safety of students and teachers.