I've installed a RAID5 using mdadm yesterday. Since then it has been rebuilding.
I just restarted my computer and it started rebuilding the RAID from scratch. (Had 60% before.) Is this normal or are there any settings missing?
The only thing I did besides creating the RAID, was adding this line to /etc/mdadm/mdadm.conf:
ARRAY /dev/md0 level=raid5 num-devices=3 UUID=bce3de1f:...:466da02f
Yes, that's normal if building the RAID wasn't done yet.
RAID 5 needs at least n-1 disks to be "built" completely (where "n" is the total number of disks in the RAID). As this was the first time you were (re)building them, all of them were only built for 60%, and none of them were marked as "complete".