Hi, my cat is 1 n half yrs old. Very healthy and very active. She is completely litter trained but from last 2 days she is showing unusual behavior she pee on sofa,my bed pillow, foot mat,floor etc. I'm worried why she is doing so? There is no change in her diet as well. Please help me out I'm waiting for your reply.

Hi fairy and welcome,
she is showing unusual behavior

I thought this was usual for cats. Jokes aside, post whether she has been fixed and the pet experts will be along with good advice. Good luck

She could possibly have a urinary tract infection, often a cat will associate the discomfort of a UTI with the litterbox and refrain from using it.
It could also be that she simply doesn't like the litter in her box.
You should take her in for a urine check and rule the medical out first and go from there.
Also is she spayed?

Important to keep letterbox extremely clean as this is where UTIs start in cats.

Also do you have other pets? Sometimes animals will mark their territory. Or if it happens only when you are not home it could be separation anxiety disorder.