Anthony Alastair Johnstone (born 2 May 1956) is a Zimbabwean professional golfer.

Johnstone was born in Bulawayo, Rhodesia and attended Christian Brothers College. He lives in Sunningdale in England. He turned professional in 1979 and has spent his career playing mainly on the Southern African Sunshine Tour and in Europe. He won six times on the European Tour and finished a career best seventh on the European Tour Order of Merit in 1992. His most prestigious win came at the 1992 British PGA Championship. He won seventeen times on the Sunshine Tour, including one co-sanctioned event also included in his European Tour win tally, and he topped that tour's Order of Merit in 1988/89 and 1993/94. He has represented Zimbabwe in international competition many times.

In 2004 Johnstone was diagnosed with multiple sclerosis, possibly ending his playing career. With a revolutionary drug treatment, he appears to have put his MS in remission and made his European Seniors Tour debut shortly after turning fifty in 2006. In 2008 he won his first EST event, the Jersey Seniors Classic. He won his second event on the Seniors tour in 2009 at the Travis Perkins plc Senior Masters.

Johnstone is noted for his excellent short game and topped the European Tour's short game statistics in 1998, 1999 and 2000. He has also worked as a golf broadcaster.