  The electrical transport and thermoelectric properties of K_xSr_{1-x}Fe_2As_2
are investigated for 0<x<1. The resistivity rho(T) shows a crossover from Fermi
liquid-like temperature dependence at small x to linear rho~T dependence at
x_c=0.4. With further increasing x, rho(T) becomes non-linear again. The
thermoelectric power S(T) exhibits a similar crossover with increasing x with a
logarithmic T-dependence, S/T~ln(T), near the critical doping x_c. These
results provide evidence for a quantum critical behavior due to the coupling of
low-energy conduction electrons to two-dimensional spin fluctuations.
