I am a non US resident and not a US citizen. I live outside US. I don't have any relation with United States. I just visit US often for pleasure only. I sell items on eBay and my items are NOT in US.
I wonder if I have to pay any tax if I open a bank account in US and withdraw money from my PayPal account to my US bank account. Likewise, do I have to pay any tax if I withdraw cash from that bank account in US?
Although there are occasional cases where simply moving money between countries results in a tax liability - for example a "non-domiciled" UK resident using the "remittance basis" - this is not the case in your situation.
In general it would be extremely rare for non-residents of a country to be taxed on bringing money into that country, as it would be bad for tourism which most countries want to encourage.
The requirement to declare large sums of money on entry is primarily so that the authorities can detect money laundering, rather than tax.
Note that you will have to pay US tax on any interest you earn on that US bank account.
