The problem is that you don't have the GPIO module installed in your virtual environment. To correct this, run the following from within your virtual environment:
for Python 2
pip install RPi.GPIO
or for Python 3
pip3 install RPi.GPIO
This will install the module where your virtual environment can find it.
One of the features of virtual environments is that they allow you to manage modules on a project by project basis and avoid conflicts with other projects (e.g. project aA requires version 1 and project B requires version 3 of the same module). More info on virtual environments and modules can be found in the Python documentation. Tutsplus has a nice tutorial on Python Virtual Environments