They're similar in that they're both compile-time functions that generate code, but they're very different in practice, because C macros are written in a text substitution language that knows virtually nothing about C, which naturally makes writing even simple macros very error-prone. Lisp macros, on the other hand, are written in plain old Lisp and receive regular Lisp data structures that you can use the whole language to operate on.

A lot of people learn from C that macros are very difficult to get right, so it's important when they move to Lisp that they give them a second look, because Lisp is a much more capable language for code transformation than cpp.

I haven't used Clojure macros but as a programmer that uses both C and Common Lisp, I can say with good authority that C macros and CL macros are very different.