  We report ac susceptibility and high-frequency electron spin resonance (ESR)
measurements on the geometrically frustrated compound
Ba$_3$NbFe$_3$Si$_2$O$_{14}$ with the N\'{e}el temperature $T_N=27 K$. An
unusually large frequency-dependence of ac susceptibility in the temperature
range of 20 - 100 K reveals a spin-glass-like behavior, signalling the presence
of frustration related slow magnetic fluctuations. ESR experiments show a
multi-step magnetic and spin chirality ordering process. For temperatures above
30 K, the weak temperature dependence of the ESR linewidth $\Delta
H_{pp}\propto T^{-p}$ with $p=0.8$ evidences the development of short-range
correlated spin clusters. The critical broadening with $p =1.8$, persisting
down to 14 K, indicates the coexistence of the short-range ordered spin
clusters within a helically ordered state. Below 9.5 K, the anomalously large
decrease of the linewidth reveals the stabilization of a long-range ordered
state with one chirality.
