Average commoner for D&D is going to be, we'll say a laborer. Bog standard, normal NPC array. Pertinent combat data only.
Str 13
Dex 11
Con 12
Wis 8
Int 10
Cha 9
AC 10
HP 8
Atk +1
Init+0
Feats: Skill Focus (chosen profession), Toughness
Dam: 1d8+1 (we'll assume they're not a total twit and using a morningstar, the best simple weapon they have access to.)
Then there's the average World of Synnibarr 'Commoner' who has 3 levels of a PC class because it's goddamn Synnibarr. . .therefore, they don't count, due to being unfairly great at everything.
M&M2e, common man is a 'Bystander'
10s in all stats, +0 to hit, AC 10, only skills are Knowledge: (Current Events) and Pop-Culture, and 4 ranks in their chosen Profession.
Note: It's possible that 'bystanders' are in fact a terrible example of a 'common man', as there are also examples for Police Officers, Fire Fighters, and other normal real-world professions that are far more competent than a faceless 'Joe Blow'.
I actually will not be surprised if the average D&D Human Commoner is more competent/dangerous than most other system/worlds ones, simply due to the fact that they tend to have to put up with more bullshit than everyone else. Goblins and the like.
As far as the 2nd Edition Shadowrun book, the closest I can find to 'A Commoner' would be The Bartender.
Body: 4
Quickness:3
Strength: 4
Charisma: 3
Intelligence: 2
Willpower : 2
Essence: 6
Reaction: 2
Professionalism: 1
Firearms: 3
Unarmed Combat: 3