Going by the facts your case, you are a NRI whose primary income source is salary which is earned outside India and therefore not taxable in India until you remain a NRI.
Now when you invest a portion of this income in US stocks, any potential income tax implications in India needs to be viewed at the time of sale of those stocks.
1. In case you are a resident in India at the time of sale, then your global income for the year will become taxable. The default capital gains tax rate for a resident Indian if you hold those stocks for more than 24 months is 20% and the gains would be computed after deducting indexed cost of purchase from net sale proceeds. If holding period is less than 24 months, it would be charged as per your normal slab rates. Moreover, this income may be taxed in US on the basis of source rule and you need to resort to beneficial provisions of DTAA to reduce double taxation and claim credit of taxes paid outside India.
2. If you are still a NRI at the time of sale of those stocks, then as per DTAA (which will override due to its beneficial provisions over domestic law) just the receipt of withdrawal proceeds in India shouldn't make it taxable here as it is neither the source nor residence country for income & assessee in question. However going by the past experience the department can still try to raise query over this. Therefore, if possible, I would suggest you to provide your Oman bank account details to stock broker for receipt of such sale proceeds and then further remit it to your NRE account to avoid potential issues from department.
Second, its good to keep your bank statements and salary certificates saved as they can help explain the source of funds and trail of transaction at the time of responding to any potential query.
For detailed discussion and end to end tax planning in this regard, I would advice you to take a telephonic consultation.