A non-resident alien files a form 1040-NR to report and pay US income tax on US-sourced income.  US-sourced income is generally income paid to you while you are living and working in the US, regardless of the location of the employer.  (In contrast, if you live overseas and work for a US-based employer, that is not US-source income for this purpose.)

You can review the table here for other types of income.

https://www.irs.gov/individuals/international-taxpayers/nonresident-aliens-source-of-income

Your question is not clear and I don't know what you mean exactly by "salary is coming from US job being done remotely?"  If you are living in the US and getting paid in the US, it's US income, even if you work at a different location than your employer.  Otherwise, you would need to give more details. 

@Opus 17 Thanks for your response.

I am currently working from outside USA for my US employer due to the travel ban restrictions and getting paid.

I have been inside USA for just a month this year which means I do not pass Substantial Presence Test. Am I liable to pay Federal/SSN/Medicare taxes for the income earned from US based employer although I am not in US physically? 

@shivanimehrotra0  Please note that a nonresident alien cannot use TurboTax. If you do have to file a U.S. tax return, you have to file Form 1040-NR, which TurboTax does not support.

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@shivanimehrotra0 wrote:

@Opus 17 Thanks for your response.

I am currently working from outside USA for my US employer due to the travel ban restrictions and getting paid.

I have been inside USA for just a month this year which means I do not pass Substantial Presence Test. Am I liable to pay Federal/SSN/Medicare taxes for the income earned from US based employer although I am not in US physically? 

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Based on the table I linked above, income paid to you by a US employer while you are overseas is not US-source income.  You would not owe income tax.  If income tax is being withheld, you would have to file a tax return to get it refunded.  Also, any part of your salary that was paid to you while in the US for that month will be US-source income and subject to tax.

If you don't pass the substantial presence test, you file a form 1040-NR which is not provided by Turbotax so you would need to find another tax software company. 

@Opus 17 Thanks for guidance. Is it true only for federal income tax or for social security/medicare tax also for the period outside US? 

It's a bit tricky to find the answer, since all the IRS documents are written to assume that the person reading them is subject to US tax law.  What I have found is that "wages" are subject to Medicare and Social Security Tax, but that "Compensation paid to a nonresident alien (other than a resident of Puerto Rico) for services performed outside the United States is not considered wages and is not subject to withholding."

So your pay, at least when you are outside the US, is not "wages" under US tax law and is not subject to any withholding.