Most motorbikes are like most computers, in that their "engines" are air cooled. Motorbike engines have large metal fins around them and air passing over the fins cools the motor as the bike rides along.
Similarly, computers have a "heat sink" on components that generate a lot of heat, and they usually also have a fan pulling air across the heat sink to more efficiently dissipate the heat.
|CPU heatsink and fan|
Motorbikes generate a lot of heat through internal combustion, and computer chips can generate a surprising amount of heat as they process the data flying through them. Both motorbikes and computers can also be cooled by liquids too, however. A motor bike can have a radiator much like an automobile; this is usually available on bigger, cruising bikes.
Computers can actually be liquid cooled as well, even though having liquid running around in a computer sounds counter intuitive (or just plain dumb). These sealed systems are typically used in high-performance computers, and although it's an expensive option, it is efficient and can be very quiet as no high speed cooling fans are needed.
Samsung is also reported to be introducing a liquid cooled smartphone, if you can believe that.
MakeTechEasier has a nice overview on the liquid cooling of PCs.