Malalai Joya was suspended by parliament on May 21 for saying parliament was less useful than a donkey or a cow.
Human Rights Watch said members of the Afghan parliament regularly criticized each other, but no one else had been suspended.
It said the Afghan parliament should revise rules restricting freedom of speech.
The rights group describes Joya as a "staunch defender of human rights and a powerful voice for Afghan women."
(with material from AFP)