Aghla Beg () is a mountain in County Donegal, Ireland. Of its two summits, one has a height of , and the other, Aghla Beg South Top .
The mountain is the third-most northern and fifth-highest of the mountain chain, called the Seven Sisters by locals: Muckish, Crocknalaragagh, Aghla Beg, Ardloughnabrackbaddy, Aghla More, Mackoght (also known as 'little Errigal') and Errigal. The Seven Sisters are part of the Derryveagh Mountains.