It depends what you mean by "science". C.S. generally does not use the scientific method, and so it is not science in the specific sense. However, it fits nicely with broader definitions; see, for example, Wiktionary's current definition #2 of "science":

> A particular discipline or branch of learning, especially one dealing with measurable or systematic principles rather than intuition or natural ability.

'Computer science' is a blanket term for parts of mathematics, engineering, and physics. To the extent that computer science falls under the realm of physics (eg, information theory and its relationship to thermodynamics), yes, it is a real science.