You can check the status from the terminal with `diskutil cs info /Volumes/<name>` and look for `Conversion State` and `LV Conversion Progress`. If you want to cancel the encryption with `diskutil cs revert /Volumes/<name>`

    srv:~ onik$ diskutil cs info /Volumes/OSX
    Core Storage Properties:
       Role:                       Logical Volume (LV)
       UUID:                       00000000-0000-0000-0000-000000000000
       Parent LVF UUID:            00000000-0000-0000-0000-000000000000
       Parent LVG UUID:            00000000-0000-0000-0000-000000000000
       Device Identifier:          disk1
       LV Status:                  Online
       Conversion State:           NoConversion
       LV Conversion Progress:     100%
       Content Hint:               Apple_HFS
       LV Name:                    OSX
       Volume Name:                OSX
       LV Size:                    126804688896 B