Numba is part of the Anaconda Python distribution. If Number is not already installed, you can install it manually using the command below.
conda install numba
Numba supports CUDA-enabled GPUs with compute capability 2.0 or above with an up-to-data Nvidia driver. You can still use Numba without a CUDA-enabled GPU using the CUDA simulator, however you will not get the performance benefits of running on a GPU.
In order to use the Numba CUDA support you will need the CUDA toolkit installed. Since you are using Anaconda, just type:
$ conda install cudatoolkit
It is also possible to install the CUDA Toolkit directly from NVIDIA, however this may require additional configuration to enable it to work with Numba so is not recommended.