Files with eeg suffix can be usually found as medical eeg (Electroencephalography) graphs or other data files.
EEG file extension - EEG data file
What is eeg file? How to open eeg files?
File type specification:
File extension eeg seems to be mainly used for stored data files from Electroencephalography (EEG) devices, for example SleepScan and Ceegraph produced by the Bio-logic Systems Corp.