Heki (2011) reported that the Japanese Global Positioning System (GPS) dense network detected a precursory positive total electron content anomaly (TEC), with ΔTEC ~3 TECU, ~40 minutes before the Tohoku-Oki earthquake (Mw 9.0). Similar preseismic TEC anomalies were also observed in the 2010 Chile earthquake (Mw 8.8), 2004 Sumatra-Andaman (Mw 9.2) and the 1994 Hokkaido-Toho-Oki (Mw 8.3). In this paper we apply our improved lithosphere-atmosphere-ionosphere (LAI) coupling model to compute the TEC variations and compare the simulation results with the reported TEC observations. For the Tohoku-Oki earthquake simulations we assumed that the stressed associated current started ~40 minutes before the earthquake, linearly increased and reached its maximum magnitude at the time of the earthquake main shock. It is suggested that a dynamo current density of ~25 nA m^-2 is required to produce the observed ΔTEC ~3 TECU.