What you need to do is declare a variable that represents your "CPU" fighter's possible states; ie: punch, kick, block, seek, flee, stand-still - and assign a number (percentage) that represents each of these. Then at each iteration where you check your actions you would generate a random number and check it against the action's number.
Here's some psuedo code to show you what I mean:

**start code**

Stand = 15;
Seek = 25;
Flee = 35;
Punch = 50;
Kick = 70;
Block = 99;

RanNumbr = generate random number here

if (RanNumbr <= 15)
Stand
else if (RanNumbr <=25)
Seek
else if (RanNumbr <= 35)
Flee
else if (RanNumbr <= 50)
Punch
else if (RanNumbr <= 70)
Kick
else if (RanNumbr > 70)
Block
end

**end code**

Of course this is generalizing it a bit, but you should get the idea. Hope this helps.