Yes, ethidium bromide is mutagenic.

Ethidium bromide (EtBr) is a flat, planar molecule with a ring structure that closely resembles a DNA base pair. This unique structure allows the EtBr molecule to intercalate between stacked bases in dsDNA, unwinding the DNA and distorting its structure, flexibility, and charge. These distortions interfere with DNA replication, transcription, recombination, and repair, leading to various mutations.