I agree with the answer from ymb1, but I think that the underlying rationale would be useful to add as well. I've looked into lightning strike protection a little bit for a small helicopter design project I worked on and am drawing from that and a useful article from Composite World (http://www.compositesworld.com/articles/lightning-strike-protection-strategies-for-composite-aircraft).
Insofar as I understand it, lightning is always attempting to get to a ground (i.e., to the lowest potential state possible), and an airplane provides a possible location for leaders (some explanation here: http://www.srh.noaa.gov/srh/jetstream/lightning/lightning_max.html - the gist is that you get an electrical channel forming from both endpoints when you have a lightning strike) going from the ground to the cloud or vice versa to form -- and at a much closer distance to both, increasing the possibility for a strike to occur with the aircraft in the middle of it. This is especially true for airplanes with metal or otherwise conductive skin, such as carbon fiber.
With respect to the question asked, I think that the relative ability of carbon fiber to conduct electricity is a tricky one to answer and is, perhaps, too simplified. Composites are those wonderful materials that can be formulated just about any way you want to give whatever properties you want. For example, a representative sample of the carbon fiber material from the tail boom for my model airplane is going to behave incredibly differently when compared to a sample of the carbon fiber material on the leading edge of the space shuttle. Each has been weaved in the different way, fibers are in different orientations, different additives have been thrown in, perhaps even additional or different fibers have been added to obtain different desired structural or electrical properties, flame resistance, or corrosion resistance. Hence, saying whether or not a carbon fiber airframe is more conductive than aluminum is not really a straightforward question. The important thing, though, is that it DOES conduct electricity and that can be problematic.
Hence the importance of lightning strike protection (LSP) measures. If you don't have an LSP system, your skin becomes the route upon which the electricity can travel, causing damage ranging from burned off paint to scorched skin material to holes burned in the airframe to delaminated composite members. What LSP does is create an alternative, low-resistance path for the lightning to follow between entry and exit points in an effect to plan where your damage is going to be and mitigate it.