The Icelandic Meteorological Office found a small volcanic eruption under the ice gap of a glacier at the volcano, which is situated in central Iceland.
The office raised its aviation alert at the site to red, signifying that an eruption is in progress.
It's not clear if Bárðarbunga will erupt above the glacier, though scientists have recorded an increase in seismic activity in the area. The volcano last erupted in 1910.
In 2010, Iceland's Eyjafjallajokull volcano erupted, disrupting European air travel.