Hi,
Please check out below code:
<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
<asp:RegularExpressionValidator ID="reg" runat="server" ControlToValidate="TextBox1" ErrorMessage="This character is not allowed" ValidationExpression="^[^*%']+$">
</asp:RegularExpressionValidator>
Mark as solved if it helps you.
Thanks,
KK