I am using testnet for testing the transactions, can we use same wallet address for the mainnet ?
Thanks,
Zeeshan
Yes, the mnemonic will result in the same address in either network. You can test it in a wallet or with the SDK.
Got it, thanku very much.
However, it is always recommended to have a wallet for the Testnet and one for the Mainnet. 
Adding to what @Tim mentioned above, that while you could use the same public/private key for multiple networks, the transaction you generate would always have a different IDs, since the transaction encoding includes the chain’s genesis hash and genesis id. ( i.e. hence, there is no security issue involved in having the same key on multiple chains )