Robb is a surname of Scottish origin, formed from a diminution (reduction) of the name Robert. Robert was a popular name, especially after its use by three Scots Kings in the fourteenth century. Rob is first recorded as a surname in the mid-15th century, with a handful of individuals recorded in the decades either side of 1500. As the 16th century progressed there were early groupings in Aberdeenshire, Lanarkshire and later in Perthshire/Stirlingshire.
https://en.wikipedia.org/wiki/Robb