A simple cyst in the liver is a very benign cyst, (a swelling like a balloon containing some clear fluid), usually small and lot of people have them. Sometimes it can be associated with similar cysts in other organs, like kidney, etc. and is of no consequence.
Other cysts, i.e., larger and multi-locular cysts can be due to infection, bacterial or amoebic and several other infections or infestations. CT scan is the right investigation to learn more about the nature of the cyst in order to aim treatment as appropriate.