Tsuyoshi Ito answered the question literally, but I wanted to comment about the semantics of MA and PCP and how they differ.
MA is the probabilistic version of NP, i.e., the verifier gets to also use poly-many random bits.
In PCP we may refer to the "randomness" of the verifier, but usually the randomness is logarithmic in the running time of the verifier, i.e., the verifier could have tried all possible random strings by itself. In other words, this "randomness" doesn't buy the verifier any computational power, unlike the case of MA.
[So what is this "randomness" good for? The point of PCP is that for probabilistic verification a single test --with a constant number of queries to the proof-- suffices]
Addendum (following Tsuyoshi's comment): In PCP characterizations of NP the verifier's running time can be made poly-logarithmic, and, similarly, in characterizations of NEXP the verifier's running time is polynomial. Nonetheless, the randomness in PCP constructions is typically used only to pick a test (in characterizations of NP, out of poly-many tests, and in characterizations of NEXP, out of exponentially many) and not to help with the computation. Moreover, in MA, the proof is of polynomial size, while in characterizations of NEXP, the proof is of exponential size.