Scientists have formulated at least 100 definitions of intelligence. (for a partial listing see www.vetta.org/definitions-of-intelligence/)
Several computer programs exist which qualify as intelligent according to at least the vast majority of these definitions. (for instance my Asa,
Trans. of the Kansas Acad, of Sci., vol. 109, # 3/4, pg 159, 2006,
www.bioone.org/archive/0022-8443/109/3/pdf/i0022-8443-109-3-159.pdf)
Not all creatures are equally intelligent so there is no need for an AI to be as intelligent as the average human. In point of fact, however, AIs exist which outperform humans at a number of important tasks.