Carl Natanael Rexroth-Berg (9 February 1879 – 14 October 1957) was a Swedish composer.

Berg was born and died in Stockholm. He trained in veterinary medicine and began learning music by teaching himself. He later studied at the Stockholm Conservatory. Until 1939, he served as a veterinarian in the Swedish Army and afterwards became a freelance composer.

His output included five operas, three ballets, five symphonies as well as several symphonic poems, a piano concerto, a violin concerto, a serenade for violin and orchestra, a piano quintet, ballades, lieder, and pieces for piano.