Answer: Yes, you can install travertine pavers on top of concrete. You can either use a 1/2 inch to 1 inch sand bed for a dry-set installation or thin set (wet set) over concrete. More installation information can be found here: Travertine Installation
Please note: In freeze/thaw climates, sand-set is the only recommended installation method. If you need to mortar the travertine, use a flexible mortar such as Flex-Bond.