A frame usually does not block keyboard inputs.
Lua Code:
local frame = CreateFrame("Frame", "SomeFrame" _G.UIParent);
frame:SetSize(50, 50);
frame:SetPoint("CENTER");
frame:SetBackdrop({bgFile = "Interface/Tooltips/UI-Tooltip-Background",
edgeFile = "Interface/Tooltips/UI-Tooltip-Border",
tile = true, tileSize = 16, edgeSize = 16,
insets = { left = 4, right = 4, top = 4, bottom = 4 }});
Above code creates a 50 x 50 frame in the middle of the screen.
It wont block any keyboard inputs.