Johann August Just (c. 1750 in Gröningen, Holy Roman Empire – December 1791? in The Hague) was a German keyboard player, violinist and composer.

He wrote a number of works for keyboard and chamber ensembles, many of a pedagogical nature, and at least two one-act operas.

He became music master to the Princess of Orange.

There is much uncertainty about his date of birth (variously given as 1750, 1758, or 1760) and date and place of death. It appears that he was born in Gröningen in Germany, but a number of reference articles have confused this with Groningen in the east of the Netherlands.

Some of his works have been recorded by the German ensemble Trio 1790.