The concept of active medium is used as a biophysical basis for modeling spatial and temporal self-organization in anthropogenic ecosystems that results in formation of regular dynamic structures with stable or unstable modes of development. Urban ecosystem is represented as a hierarchy of interacting active media, and their non-linearity is the result of extreme anthropogenic load and mismatch between characteristic times and scales in evolution of the natural and anthropogenic components together with the complex set of positive and negative feedbacks between the subsystems. Description of the presented model is deliberately simplified so as to use a modified Fitz-Hugh-Nagumo equation. The approach developed here is quite general and allows for systematic description of urban ecosystems as distributed dissipative systems.