A method and system for detecting a suspicious frame in a wireless sensor network that includes: a plurality of sensor nodes, for sending sensed data and data regarding an upper-level node and cluster head node. A data collecting node receives data from the sensor nodes, sends information, and extracts data received from the sensor nodes. A first probability of occurrence of the routing path is computed with respect to training frames, and a second probability of occurrence of a source routing path is computed using the first probability. The second probability is compared with a reference value, and displays an indication notifying an abnormality of the source node according to when the second probability and the reference value.