If you are wondering if it's OK to keep a pet bunny without access to a grassy area then the answer is yes they can live perfectly happily as long as you provide them with the right foods.
As most house bunny owners will tell you they live perfectly well in your home on a carpet or hard surface.
If you think your bunny is missing out on the experience of running around on grass then why not get your bunny to harness and take it to a garden or park.
Its best to get your bunny use to the harness first in your home, then when they are confident using it find a nice quite spot away from where people may walk their dogs and let them have a run around keeping a form hold of them all the time.
Alternately you could set up a pet pen and let them play in this area. Make sure they are supervised at all times as you don't want the local cat to take an interest and remember bunnies can climb and jump so make sure it has high sides or a net over the top.