(CNN) The last few months of 2018 saw an uptick in domestic terror arrests compared to some other quarters in recent years, a senior FBI official told CNN.

Nearly 25 were arrested over the last three months of 2018, said the official, citing the most recent data available.

However, when looking at yearly numbers, the FBI noted that in fiscal year 2018 -- from October 2017 to October 2018 -- it arrested 120 domestic terror suspects, and 150 the year before.

The domestic terror arrests include but are not limited to far right/white nationalists. The official did not provide an explanation for the increase in that quarter.

The FBI says it has approximately 900 open domestic terror investigations. These are separate from international terrorism investigations, which, for example, involve plots related to ISIS and al Qaeda, including so-called "lone wolf attacks." Overall the FBI says it has some 5,000 open terrorism investigations around the world, including those domestic terrorism investigations, with the rest related to international terrorism.

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