Normally, you have to turn the key to prevent this. Check for the key position.
Disabling Sun keyboard abort sequence
The default keyboard abort sequence on a Solaris system is sent with the L1-A or STOP-A keys pressed together on an attached Sun keyboard, or the BREAK signal on the serial console.
Inserting or unplugging a keyboard on a running Sun system will also send an abort sequence, effectively dropping you to the Open Boot Prompt ("ok" prompt).
To disable the keyboard abort sequence for the current session:
kbd -a disable
To disable the keyboard abort sequence for future sessions (i.e. after a system reboot), change the following in /etc/default/keyboard.