  Local structure of NdFeAsO$_{1-x}$F$_{x}$ ($x$=0.0, 0.05, 0.15 and 0.18) high
temperature iron pnictide superconductor system is studied using arsenic
$K$-edge extended x-ray absorption fine structure measurements as a function of
temperature. Fe-As bondlength shows only a weak temperature and F-substitution
dependence, consistent with the strong covalent nature of this bond. The
temperature dependence of the mean-square relative-displacements of the Fe-As
bondlength are well described by the correlated-Einstein model for all the
samples, but with different Einstein-temperatures for the superconducting and
non-superconducting samples. The results indicate distinct local Fe-As lattice
dynamics in the superconducting and non-superconducting iron-pnictide systems.
