The immediately surrounding area is called Exarcheia and the closest Metro station is Omonia, which is less than 10 minute walk (~600m) to NTUA.
FROM THE AIRPORT
Taking the Metro from the airport is the easiest way to get into Athens. It runs from 6.30 to 23.30 every 30 minutes and takes about 45min. You take Line 3 (Blue) to Syntagma Square, then change to Line 2 (Red, direction Agios Antonios) for a couple of stops to Omonia Square. The ticket costs 10 euros.
Take bus X95 (just outside arrivals) to Syntagma (terminal). Buses run every 10 minutes during day and every 20 minutes the whole night. The ticket costs 6 euros.
Taxi from the airport to the centre will cost you 35 euros during daytime and 50 euros after midnight (fix price).