German: Ottokar Eugen Nováček (Czech: Otakar Evžen Nováček, Hungarian: Nováček Ottokár Jenő); May 13, 1866, Fehertémplom (German: Weißkirchen, Serbo-Croatian: Bela Crkva), southern Hungary – February 3, 1900, New York City) was an Hungarian violinist and composer of Czech descent and is perhaps best known for his work Perpetuum Mobile (Perpetual Motion). 

Novacek studied successfully with his father Martin Joseph Nováček, with Jakob Dont in Vienna (1880-83), and with Henry Schradieck and Brodsky at the Leipzig Conservatory, where he won the Mendelssohn Prize in 1885. He played in the Leipzig Gewandhaus Orchestra and in the Brodsky Quartet, originally as second violin and later as viola. He subsequently immigrated to the USA, where he was a member of the Boston Symphony Orchestra under Arthur Nikisch (1891) and was appointed principal viola in the Damrosch Orchestra, New York (1892-3). He also played in the re-formed Brodsky Quartet.

In 1899, after a heart condition forced him to retire from playing, he devoted himself to composition. His works include a piano concerto (1894, first performed by Ferruccio Busoni), Perpetuum mobile (Perpetual Motion) for violin and orchestra, three string quartets (published in 1890, 1898 and 1904), eight Concerto caprices and other works for violin and piano, and six songs to texts by Leo Tolstoy.