Hofsfjökull volcano is not among the most activate volcanoes in Iceland. It has never erupted since Iceland got inhabited. The last eruption that took place in Hofsjökull volcano is undated, but took place sometimes in the last 12.000 years or so.
Here is a short overview of the activity since the year 1999 in Hofsjökull volcano. All pictures are from the web site of Icelandic Met Office and copyright of them belongs to them.
Last earthquake swarm took place in Week 47, in the year 1999.
In Week 21, in the year 2008 a harmonic tremor pulse was detected from Hofsjökull volcano. This started at 13:30 UTC on the 24. May 2008.
SIL stations in Iceland showing the harmonic tremor pulse. Picture number one.
SIL stations in Iceland showing the harmonic tremor pulse. Picture number two.
Spectrograph from the SIL station Saurbær (south Iceland, located on the SISZ).
Spectrograph from the SIL station Skrokkalda. This station is located closest to Hofsjökull volcano, along with the SIL station at Hveravöllum hydrothermal area.
During this episode of harmonic tremor one earthquake was detected in north Hofsjökull volcano.
The one earthquake detected in Week 21 in the year 2008. On the week overview for Week 21 in the year 2008 they think that this might have been a swarm of small earthquakes that they where unable to locate. But I do not agree with that, given the data that is published on this event.
Other then this there have been few earthquakes every now and then in Hofsjökull volcano. But besides that it remains quiet and is most likely to be so for the time being.