Gary Gifford wrote on Sun, Dec 17, 2006 02:31 PM UTC:
Josh asks, 'May A King Attack When it is in check?'
Answer: Certainly. Thus if your opponent's Queen moves next to your King
and checks it, your King can simply take the Queen (unless your opponent
has that checking square protected by another piece of theirs.
Remember: Kings cannot move into check. Nor can they castle while in
check, nor can they castle through a check. But they can certainly capture
other [unprotected] pieces while in check.