If you get the activation key via email the instructions say: If you have not already done so, please download and unzip the software, copy the attached file 'mjkey.txt' to the 'bin' subdirectory, and then you can run the software. While if you go to https://github.com/openai/mujoco-py it says: Unzip the downloaded mujoco200 directory into ~/.mujoco/mujoco200, and place your license key (the mjkey.txtfile from your email) at ~/.mujoco/mjkey.txt. When I downloaded the linux version it came as "mujoco200_linux" and I then also had to change its name. Something in the email with the activation key that notes the install instructions for using mujoco-py may be helpful and less confusing to new users.