is the lassen peak in California active or dormant?

Answer 1

It is very recently active, but not currently erupting. It will probably erupt again. By some definitions, a volcano that is not erupting is "dormant" if it will probably erupt again. By other people's definitions, a volcano is active if it has erupted in recent history. So, Lassen is "dormant" or "active" depending on how you define the word "dormant".
For several years after the May 22, 1915, eruption, spring snowmelt percolating down into Lassen Peak triggered steam explosions, indicating that rocks beneath the volcano’s surface remained hot. Particularly vigorous steam explosions in May 1917 blasted out the second of the two craters now seen near the volcano’s summit. Steam vents could be found in the area of these craters into the 1950’s but gradually waned and are difficult to locate today. Lassen Peak sleeps again, but active steam vents, hot springs, and bubbling pools of hot mud are still found elsewhere in Lassen Volcanic National Park. No one can say when, but it is almost certain that the Lassen area will experience volcanic eruptions again.
http://pubs.usgs.gov/fs/1998/fs173-98/
http://pubs.usgs.gov/fs/2000/fs022-00/

Answer 2

Dormant