They were allegedly planning attacks aginst a festival which began with the start of the Eid al-Adha. The festival will end on 18th February and roughly two million are expected to participate. It seems a cargo of arms has also been seized. The last arrests of this kind in Oman were in 1994.
I write about this because I lived in Oman for several years, and in a number of adjacent countries for similar periods. Until now Oman has not been regarded as a potential target for extremists.