It appears to be fairly common, yes. Have a look at the Wikipedia article on software versioning.
Quote below is from that page:
Designating development stage
Some schemes use a zero in the first sequence to designate alpha or beta status for releases that are not stable enough for general or practical deployment and are intended for testing or internal use only.
It can be used in the third position:
0 for alpha (status)
1 for beta (status)
2 for release candidate
3 for (final) release
220.127.116.11 instead of 1.2-a1
18.104.22.168 instead of 1.2-b2 (beta with some bug fixes)
22.214.171.124 instead of 1.2-rc3 (release candidate)
126.96.36.199 instead of 1.2-r (commercial distribution)
188.8.131.52 instead of 1.2-r5 (commercial distribution with many bug fixes)