We use explicit atom molecular dynamics to investigate mobility in poly(methyl methacrylate) [PMMA] when blended with 10%, 20%, and 30% weight percent poly(ethylene oxide) [PEO]. The responses to blending of main chain motion, rotation of the two methyl groups, and rotation of the entire ester side chain, which is associated with the P-relaxation, are individually assessed at temperatures well above the glass transition temperature where their characteristic times overlap. We also consider the response of main chain motion in PEO to blending with PMMA. We find three classes of behavior: methyl group rotation is not influenced by blending, ester group rotation and the main chain motion of PEO are slightly altered by the change in environment, and a substantial change in dynamics is observed for main chain motion in PMMA. The observation that the P-relaxation in PMMA changes with mixing is unusual, as this is a local motion thought to be insensitive to blending. This is discussed in light of the spatial extent of localized motion and that of mixing of the two components.