The fsck(1M) command is checking the filesystem shown in the messages that are displayed before this one. The first phase checks the inode list, finds bad or duplicate blocks, and verifies the inode size and format.
If more than a dozen errors occur during this important phase, you might want to restore the filesystem from backup tapes. Otherwise it is fine to proceed with fsck(1M).
For more information, see the chapter on checking filesystem integrity in the System Administration Guide, Volume I.