Our cat is diagnosed epileptic and is on phenobarbital. Sometimes she has these small seizures, even on the meds. (she also has a full on seizure every 2 or 3 months before medication it was every 2 weeks!)
Watch out for the eyes screwing up and ears flattening every so often.

Edit: I am very sorry to say that our cat Pixel died in December 2012 after entering status epilepticus, despite rushing her straight to the vet who managed to bring her out of the seizure, she suffered another one shortly afterwards from which she was unable to recover. We miss her terribly.