Although it has been proven already in 2005 [1] that catalytic P systems with two catalysts are computationally universal, no simple example of such a P system generating a non-semilinear set was known. The present paper intends to fill this gap and provides such an example with 54 rules. It is expected, however, that this number of rules can be dramatically reduced and the minimal number of rules to generate a non-semilinear set in a catalytic P system with two catalysts remains open.