In OTC market Collateral Posting as cash is normal, so when it is said
Collateral Posted as USD CASH
Does that mean Actual amount of currency is posted electronically (or any security is posted) and does it carry any interest Rate Risk?
It means that cash is posted electronically. The party receiving the cash must pay interest on it, usually Fed Funds on an overnight basis in the US, specified in the CSA (credit support annex).